Merge pull request #7899 from dcw803/master

belatedly did and committed my solutions to challenge 211

16 files changed, 1001 insertions, 57 deletions

diff --git a/challenge-205/duncan-c-white/C/README b/challenge-205/duncan-c-white/C/README
index 79d015ffe4..1e1acd8915 100644
--- a/challenge-205/duncan-c-white/C/README
+++ b/challenge-205/duncan-c-white/C/README
@@ -3,11 +3,6 @@ Thought I'd also have a go at translating ch-1.pl and ch-2.pl into C..
 Both C versions produce near-identical (non-debugging and even debugging)
 output to the Perl originals.
 
-The C translation of ch-2.pl was quite tricky to write, mainly on storage
-allocation (as usual), although I found a neat (slightly cheaty?)
-way of doing it.  specifically: I create a 1d-array of all the elements,
-and then I print it out as if it were an RxC matrix..
-
 These C versions use most of my regular support modules:
 - a command-line argument processing module args.[ch],
 - a csvlist-of-int parsing module parseints.[ch], and
diff --git a/challenge-210/duncan-c-white/README b/challenge-210/duncan-c-white/README
index 6013657b55..8bb0290387 100644
--- a/challenge-210/duncan-c-white/README
+++ b/challenge-210/duncan-c-white/README
@@ -1,4 +1,4 @@
-Task 1: Task 1: Kill and Win
+Task 1: Kill and Win
 
 You are given a list of integers.  Write a script to get the maximum points.
 You are allowed to take out (kill) any integer and remove from the list.
diff --git a/challenge-211/duncan-c-white/C/.cbuild b/challenge-211/duncan-c-white/C/.cbuild
index 835981f6f1..a14ec76520 100644
--- a/challenge-211/duncan-c-white/C/.cbuild
+++ b/challenge-211/duncan-c-white/C/.cbuild
@@ -1,5 +1,4 @@
 BUILD = ch-1 ch-2
-BUILD = ch-1
 CFLAGS = -Wall -g
 #LDFLAGS = -lm
 #CFLAGS = -g
diff --git a/challenge-211/duncan-c-white/C/Makefile b/challenge-211/duncan-c-white/C/Makefile
new file mode 100644
index 0000000000..1b34ccd3b2
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/Makefile
@@ -0,0 +1,18 @@
+# Makefile rules generated by CB
+CC	= gcc
+CFLAGS	= -Wall -g
+BUILD	= ch-1 ch-2
+
+all:	$(BUILD)
+
+clean:
+	/bin/rm -f $(BUILD) *.o core a.out
+
+args.o:	args.c
+ch-1:	ch-1.o args.o parseints.o printarray.o
+ch-1.o:	ch-1.c args.h parseints.h printarray.h
+ch-2:	ch-2.o args.o parseints.o printarray.o
+ch-2.o:	ch-2.c args.h parseints.h printarray.h
+parseints.o:	parseints.c args.h parseints.h printarray.h
+printarray.o:	printarray.c
+
diff --git a/challenge-211/duncan-c-white/C/README b/challenge-211/duncan-c-white/C/README
new file mode 100644
index 0000000000..341becc1e1
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/README
@@ -0,0 +1,9 @@
+Thought I'd also have a go at translating ch-1.pl and ch-2.pl into C..
+
+Both C versions produce near identical (non-debugging and debugging)
+output to the Perl originals.
+
+These C versions use some of my regular support modules:
+- my command-line argument processing module args.[ch],
+- my csvlist-of-int parsing module parseints.[ch], and
+- my int-array printing module printarray.[ch].
diff --git a/challenge-211/duncan-c-white/C/args.c b/challenge-211/duncan-c-white/C/args.c
new file mode 100644
index 0000000000..20c21e6c30
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/args.c
@@ -0,0 +1,234 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+
+
+bool debug = false;
+
+
+// process_flag_noarg( name, argc, argv );
+//	Process the -d flag, and check that there are no
+//	remaining arguments.
+void process_flag_noarg( char *name, int argc, char **argv )
+{
+	int arg=1;
+	if( argc>1 && strcmp( argv[arg], "-d" ) == 0 )
+	{
+		debug = true;
+		arg++;
+	}
+
+	int left = argc-arg;
+	if( left != 0 )
+	{
+		fprintf( stderr, "Usage: %s [-d]\n", name );
+		exit(1);
+	}
+}
+
+
+// int argno = process_flag_n_args( name, argc, argv, n, argmsg );
+//	Process the -d flag, and check that there are exactly
+//	n remaining arguments, return the index position of the first
+//	argument.  If not, generate a fatal Usage error using the argmsg.
+//	
+int process_flag_n_args( char *name, int argc, char **argv, int n, char *argmsg )
+{
+	int arg=1;
+	if( argc>1 && strcmp( argv[arg], "-d" ) == 0 )
+	{
+		debug = true;
+		arg++;
+	}
+
+	int left = argc-arg;
+	if( left != n )
+	{
+		fprintf( stderr, "Usage: %s [-d] %s\n       Exactly %d "
+			"arguments needed\n", name, argmsg, n );
+		exit(1);
+	}
+	return arg;
+}
+
+
+// int argno = process_flag_n_m_args( name, argc, argv, min, max, argmsg );
+//	Process the -d flag, and check that there are between
+//	min and max remaining arguments, return the index position of the first
+//	argument.  If not, generate a fatal Usage error using the argmsg.
+//	
+int process_flag_n_m_args( char *name, int argc, char **argv, int min, int max, char *argmsg )
+{
+	int arg=1;
+	if( argc>1 && strcmp( argv[arg], "-d" ) == 0 )
+	{
+		debug = true;
+		arg++;
+	}
+
+	int left = argc-arg;
+	if( left < min || left > max )
+	{
+		fprintf( stderr, "Usage: %s [-d] %s\n       Between %d and %d "
+			"arguments needed\n", name, argmsg, min, max );
+		exit(1);
+	}
+	return arg;
+}
+
+
+// process_onenumarg_default( name, argc, argv, defvalue, &n );
+//	Process the -d flag, and check that there is a single
+//	remaining numeric argument (or no arguments, in which case
+//	we use the defvalue), putting it into n
+void process_onenumarg_default( char *name, int argc, char **argv, int defvalue, int *n )
+{
+	char argmsg[100];
+	sprintf( argmsg, "[int default %d]", defvalue );
+	int arg = process_flag_n_m_args( name, argc, argv, 0, 1, argmsg );
+
+	*n = arg == argc ? defvalue : atoi( argv[arg] );
+}
+
+
+// process_onenumarg( name, argc, argv, &n );
+//	Process the -d flag, and check that there is a single
+//	remaining numeric argument, putting it into n
+void process_onenumarg( char *name, int argc, char **argv, int *n )
+{
+	int arg = process_flag_n_args( name, argc, argv, 1, "int" );
+
+	// argument is in argv[arg]
+	*n = atoi( argv[arg] );
+}
+
+
+// process_twonumargs( name, argc, argv, &m, &n );
+//	Process the -d flag, and check that there are 2
+//	remaining numeric arguments, putting them into m and n
+void process_twonumargs( char *name, int argc, char **argv, int *m, int *n )
+{
+	int arg = process_flag_n_args( name, argc, argv, 2, "int" );
+
+	// arguments are in argv[arg] and argv[arg+1]
+	*m = atoi( argv[arg++] );
+	*n = atoi( argv[arg] );
+}
+
+
+// process_twostrargs() IS DEPRECATED: use process_flag_n_m_args() instead
+
+
+// int arr[100];
+// int nel = process_listnumargs( name, argc, argv, arr, 100 );
+//	Process the -d flag, and check that there are >= 2
+//	remaining numeric arguments, putting them into arr[0..nel-1]
+//	and returning nel.
+int process_listnumargs( char *name, int argc, char **argv, int *arr, int maxel )
+{
+	int arg=1;
+	if( argc>1 && strcmp( argv[arg], "-d" ) == 0 )
+	{
+		debug = true;
+		arg++;
+	}
+
+	int left = argc-arg;
+	if( left < 2 )
+	{
+		fprintf( stderr, "Usage: %s [-d] list_of_numeric_args\n", name );
+		exit(1);
+	}
+	if( left > maxel )
+	{
+		fprintf( stderr, "%s: more than %d args\n", name, maxel );
+		exit(1);
+	}
+
+	// elements are in argv[arg], argv[arg+1]...
+
+	if( debug )
+	{
+		printf( "debug: remaining arguments are in arg=%d, "
+		        "firstn=%s, secondn=%s..\n",
+			arg, argv[arg], argv[arg+1] );
+	}
+
+	int nel = 0;
+	for( int i=arg; i<argc; i++ )
+	{
+		arr[nel++] = atoi( argv[i] );
+	}
+	arr[nel] = -1;
+	return nel;
+}
+
+
+//
+// bool isint = check_unsigned_int( char *val, int *n );
+//	Given an string val, check that there's an unsigned integer
+//	in it (after optional whitespace).  If there is a valid
+//	unsigned integer value, store that integer value in *n and
+//	return true; otherwise return false (and don't alter *n).
+bool check_unsigned_int( char *val, int *n )
+{
+	// skip whitespace in val
+	char *p;
+	for( p=val; isspace(*p); p++ )
+	{
+		/*EMPTY*/
+	}
+	if( ! isdigit(*p) ) return false;
+	*n = atoi(p);
+	return true;
+}
+
+
+//
+// bool isint = check_int( char *val, int *n );
+//	Given an string val, check that there's an integer
+//	in it (after optional whitespace).  If there is a valid
+//	integer value, store that integer value in *n and
+//	return true; otherwise return false (and don't alter *n).
+bool check_int( char *val, int *n )
+{
+	// skip whitespace in val
+	char *p;
+	for( p=val; isspace(*p); p++ )
+	{
+		/*EMPTY*/
+	}
+	int sign = 1;
+	if( *p == '+' ) p++;
+	else if( *p == '-' )
+	{
+		sign = -1;
+		p++;
+	}
+	if( ! isdigit(*p) ) return false;
+	*n = atoi(p) * sign;
+	return true;
+}
+
+
+//
+// bool ok = check_unsigned_real( char *val, double *n );
+//	Given an string val, check that there's an unsigned real
+//	in it (after optional whitespace).  If there is a valid
+//	unsigned real value, store that value in *n and
+//	return true; otherwise return false (and don't alter *n).
+bool check_unsigned_real( char *val, double *n )
+{
+	// skip whitespace in val
+	char *p;
+	for( p=val; isspace(*p); p++ )
+	{
+		/*EMPTY*/
+	}
+	if( ! isdigit(*p) ) return false;
+	*n = atof(p);
+	return true;
+}
diff --git a/challenge-211/duncan-c-white/C/args.h b/challenge-211/duncan-c-white/C/args.h
new file mode 100644
index 0000000000..df765fa21e
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/args.h
@@ -0,0 +1,12 @@
+extern bool debug;
+
+extern void process_flag_noarg( char * name, int argc, char ** argv );
+extern int process_flag_n_args( char * name, int argc, char ** argv, int n, char * argmsg );
+extern int process_flag_n_m_args( char * name, int argc, char ** argv, int min, int max, char * argmsg );
+extern void process_onenumarg_default( char * name, int argc, char ** argv, int defvalue, int * n );
+extern void process_onenumarg( char * name, int argc, char ** argv, int * n );
+extern void process_twonumargs( char * name, int argc, char ** argv, int * m, int * n );
+extern int process_listnumargs( char * name, int argc, char ** argv, int * arr, int maxel );
+extern bool check_unsigned_int( char * val, int * n );
+extern bool check_int( char * val, int * n );
+extern bool check_unsigned_real( char * val, double * n );
diff --git a/challenge-211/duncan-c-white/C/ch-1.c b/challenge-211/duncan-c-white/C/ch-1.c
new file mode 100644
index 0000000000..75cc4e6611
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/ch-1.c
@@ -0,0 +1,145 @@
+// Task 1: Toeplitz Matrix
+//
+// C translation
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+
+#include "args.h"
+#include "parseints.h"
+#include "printarray.h"
+
+
+// int nch = countch( target, str );
+//	Count and return the number of occurrences of target in str.
+//
+int countch( char target, char *str )
+{
+	int n=0;
+	for( ; *str; str++ )
+	{
+		if( *str == target ) n++;
+	}
+	return n;
+}
+
+
+// init_row( rp, rowdata, ncols );
+//	initialize the ncols values in the row (rp) from rowdata,
+//	modifying rowdata slightly (replacing ','s with '\0's)
+//
+void init_row( int *rp, char *rowdata, int ncols )
+{
+	int n = 1 + countch(',', rowdata);
+	if( n != ncols )
+	{
+		fprintf( stderr, "All rows need %d columns - not %d\n",
+			ncols, n );
+		exit(1);
+	}
+
+	char *p, *q;
+	for( p = rowdata; (q = strchr(p,',')) != NULL; p=q+1 )
+	{
+		*q = '\0';
+		*rp++ = atoi(p);
+	}
+	*rp++ = atoi(p);
+}
+
+
+// show_matrix( m, nrows, ncols );
+//	Display the given matrix.
+//
+void show_matrix( int **m, int nrows, int ncols )
+{
+	for( int i=0; i<nrows; i++ )
+	{
+		printf( "[ " );
+		for( int j=0; j<ncols; j++ )
+		{
+			if( j>0 ) putchar(',');
+			printf( "%d", m[i][j] );
+		}
+		printf( " ]\n" );
+	}
+}
+
+
+//
+// bool same = samediag(r,c,rows,cols,m);
+//	Return true iff all matrix cells in m[][] down the
+//	top-left->bottom-right diagonal starting at (r,c)
+//	are the same value; false otherwise.
+//
+bool samediag( int r, int c, int rows, int cols, int **m )
+{
+	for( int v = m[r][c]; r<rows && c<cols; r++, c++ )
+	{
+		if( m[r][c] != v ) return false;
+	}
+	return true;
+}
+
+
+//
+// bool istp = toeplitz( rows, cols, m );
+//	return true iff m[rows][cols] is a toeplitz matrix, false otherwise
+//
+bool toeplitz( int rows, int cols, int **m )
+{
+	for( int r=rows-2; r>=0; r-- )
+	{
+		if( ! samediag(r,0,rows,cols,m) ) return false;
+	}
+	for( int c=1; c<cols-1; c++ )
+	{
+		if( ! samediag(0,c,rows,cols,m) ) return false;
+	}
+	return true;
+}
+
+
+int main( int argc, char **argv )
+{
+	int argno = process_flag_n_m_args( "toeplitz-matrix", argc, argv,
+		1, 1000, "list(row)" );
+
+	int nrows = argc-argno;
+	int ncols = 1 + countch(',', argv[argno] );
+	if( debug )
+	{
+		printf( "debug: nrows = %d, ncols = %d\n", nrows, ncols );
+	}
+
+	int **m = malloc( nrows * sizeof(int *) );
+	assert( m != NULL );
+	for( int i=0; i<nrows; i++ )
+	{
+		m[i] = malloc( ncols * sizeof(int) );
+		assert( m[i] != NULL );
+		init_row( m[i], argv[argno++], ncols );
+	}
+
+	if( debug )
+	{
+		printf( "debug: matrix:\n" );
+		show_matrix( m, nrows, ncols );
+		putchar( '\n' );
+	}
+
+	bool is = toeplitz( nrows, ncols, m );
+	printf( "%s\n", is ? "true" : "false" );
+
+	for( int i=0; i<nrows; i++ )
+	{
+		free( m[i] );
+	}
+	free( m );
+
+	return 0;
+}
diff --git a/challenge-211/duncan-c-white/C/ch-2.c b/challenge-211/duncan-c-white/C/ch-2.c
new file mode 100644
index 0000000000..858d9c14f3
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/ch-2.c
@@ -0,0 +1,166 @@
+//
+// Task 2: Split Same Average
+// 
+// C version.
+// 
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <math.h>
+
+#include "args.h"
+#include "parseints.h"
+#include "printarray.h"
+
+
+#define EPSILON 0.00001
+
+
+//
+// void subset_select( comb, nval, val[], &nsel, sel[], &nnotsel, notsel[] );
+//	Consider comb as an nsel-bit binary unsigned number.
+//	Select all the values from val[] whose corresponding bit in comb is 1,
+//	store them into sel[nsel] (setting nsel), and store all the unselected
+//	values into notsel[nnotsel], setting nnotsel.
+//
+void subset_select( int comb, int nval, int *val, int *nsel, int *sel, int *nnotsel, int *notsel )
+{
+	*nsel = *nnotsel = 0;
+	for( int i=0; i<nval; i++ )
+	{
+		int v = val[i];
+		if( comb%2 == 1 )
+		{
+			sel[(*nsel)++] = v;
+		} else
+		{
+			notsel[(*nnotsel)++] = v;
+		}
+		comb >>= 1;
+	}
+}
+
+
+//
+// bool found = count_val_avg( goalavg, nval, val[], &nsel, sel[], &nnotsel, notsel[] );
+//	Attempt to find a subset of val[nval] whose average is goalavg.
+//	If we find one, copy the number of subset elements into nsel,
+//      and all subset elements into sel[nsel], and all other elements into
+//	notsel[], setting notnsel to nval - nsel, and return true.
+//	If we can't find one, return false.
+//	Do it by iterating over all D-bit binary numbers from 1..2**nval-2
+//	subset-summing each selected combination
+//
+bool count_val_avg( double goalavg, int nval, int *val, int *nsel, int *sel, int *nnotsel, int *notsel )
+{
+	// d = 2**nval - 2
+	int d = 1;
+	for( int i=0; i<nval; i++ ) d *= 2;
+	d -= 2;
+
+	if( debug )
+	{
+		printf( "debug: nval = %d, d = %d\n", nval, d );
+	}
+
+	for( int comb=1; comb<=d; comb++ )
+	{
+		*nsel = 0;
+		*nnotsel = 0;
+		subset_select( comb, nval, val, nsel, sel, nnotsel, notsel );
+		if( debug )
+		{
+			printf( "debug: selecting comb=%d, nsel=%d, "
+				"nnotsel=%d, selected = ",
+				comb, *nsel, *nnotsel );
+			print_int_array( 60, *nsel, sel, ',', stdout );
+		}
+
+		if( *nsel == 0 )
+		{
+			if( debug ) printf( " : rejected\n" );
+			continue;
+		}
+
+		int sum = 0;
+		for( int i=0; i<*nsel; i++ )
+		{
+			sum += sel[i];
+		}
+		double avg = ((double)sum) / *nsel;
+		if( debug )
+		{
+			//printf( ", not selected = " );
+			//print_int_array( 60, *nnotsel, notsel, ',', stdout );
+			printf( ", sum=%d, avg=%g\n", sum, avg );
+		}
+		if( fabs(avg-goalavg) < EPSILON )
+		{
+			#if 0
+			printf( "debug: returning true, fabs(a-ga)=%g\n",
+				fabs(avg-goalavg) );
+			#endif
+
+			return true;
+		}
+	}
+	return false;
+}
+
+
+int main( int argc, char **argv )
+{
+	int argno = process_flag_n_m_args( "split-sum-average", argc, argv,
+		1, 1000, "intlist" );
+	int nel;
+	int *list = parse_int_args( argc, argv, argno, &nel );
+
+	if( debug )
+	{
+		printf( "debug: list: " );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	int sel[nel];
+	int notsel[nel];
+	int nsel = 0;
+	int nnotsel = 0;
+
+	int sum = 0;
+	for( int i=0; i<nel; i++ )
+	{
+		sum += list[i];
+	}
+	double goalavg = ((double)sum)/nel;
+	if( debug )
+	{
+		printf( "debug: goal average is %g\n", goalavg );
+	}
+
+
+	bool found = count_val_avg( goalavg, nel, list,
+				    &nsel, sel, &nnotsel, notsel );
+	if( found )
+	{
+		if( debug )
+		{
+			printf( "debug: found selected " );
+			print_int_array( 60, nsel, sel, ',', stdout );
+			printf( " and not selected " );
+			print_int_array( 60, nnotsel, notsel, ',', stdout );
+			putchar( '\n' );
+		}
+		printf( "true\n" );
+	} else
+	{
+		if( debug )
+		{
+			printf( "debug: no subsets found\n" );
+		}
+		printf( "false\n" );
+	}
+	return 0;
+}
diff --git a/challenge-211/duncan-c-white/C/parseints.c b/challenge-211/duncan-c-white/C/parseints.c
new file mode 100644
index 0000000000..3e820eb334
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/parseints.c
@@ -0,0 +1,114 @@
+// Simple routine to parse one or more arguments,
+// looking for individual ints or comma-separated
+// lists of ints.
+// 
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+
+#include "args.h"
+#include "printarray.h"
+#include "parseints.h"
+
+typedef struct
+{
+	int nel;	// current number of elements 
+	int maxel;	// maximum number of elements allocated
+	int *list;	// malloc()d list of integers
+} intlist;
+
+
+//
+// intlist il.. then initialize il..  then:
+// add_one( element, &il );
+//	
+static void add_one( int x, intlist *p )
+{
+	if( p->nel > p->maxel )
+	{
+		p->maxel += 128;
+		p->list = realloc( p->list, p->maxel );
+		assert( p->list != NULL );
+	}
+	#if 0
+	if( debug )
+	{
+		printf( "PIA: appending %d to result at "
+			"pos %d\n", x, p->nel );
+	}
+	#endif
+	p->list[p->nel++] = x;
+}
+
+
+//
+// intlist il.. then initialize il..  then:
+// add_one_arg( argstr, &il );
+//	
+static void add_one_arg( char *argstr, intlist *p )
+{
+	int x;
+	if( !check_int(argstr,&x) )
+	{
+		fprintf( stderr, "PIA: arg %s must be int\n", argstr );
+		exit(1);
+	}
+	add_one( x, p );
+}
+
+
+//
+// int nel;
+// int *ilist = parse_int_args( argc, argv, argno, &nel );
+//	process all arguments argv[argno..argc-1], extracting either
+//	single ints or comma-separated lists of ints from those arguments,
+//	accumulate all integers in a dynarray list, storing the total number
+//	of elements in nel.  This list must be freed by the caller.
+//	Note that the list of elements used to be terminated by a -1 value,
+//	but I've commented this out from now on.
+//
+int *parse_int_args( int argc, char **argv, int argno, int *nel )
+{
+	int *result = malloc( 128 * sizeof(int) );
+	assert( result != NULL );
+	intlist il = { 0, 128, result };
+
+	#if 0
+	if( debug )
+	{
+		printf( "PIA: parsing ints from args %d..%d\n", argno, argc-1 );
+	}
+	#endif
+	for( int i=argno; i<argc; i++ )
+	{
+		assert( strlen(argv[i]) < 1024 );
+		char copy[1024];
+		strcpy( copy, argv[i] );
+		char *com;
+		char *s;
+		for( s=copy; (com = strchr(s,',')) != NULL; s=com+1 )
+		{
+			*com = '\0';
+			add_one_arg( s, &il );
+		}
+		add_one_arg( s, &il );
+	}
+
+	//add_one( -1, &il );
+
+	#if 0
+	if( debug )
+	{
+		printf( "PIA: final list is " );
+		print_int_array( 80, il.nel, il.list, ',', stdout );
+		putchar( '\n' );
+	}
+	#endif
+
+	*nel = il.nel;
+	return il.list;
+}
diff --git a/challenge-211/duncan-c-white/C/parseints.h b/challenge-211/duncan-c-white/C/parseints.h
new file mode 100644
index 0000000000..da5e145a86
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/parseints.h
@@ -0,0 +1 @@
+extern int * parse_int_args( int argc, char ** argv, int argno, int * nel );
diff --git a/challenge-211/duncan-c-white/C/printarray.c b/challenge-211/duncan-c-white/C/printarray.c
new file mode 100644
index 0000000000..ddee597df3
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/printarray.c
@@ -0,0 +1,39 @@
+#include <stdio.h>
+#include <string.h>
+
+
+// print_int_array( maxw, nelements, results[], sep, outfile );
+//	format results[0..nelements-1] as a <sep> separated
+//      list onto outfile with lines <= maxw chars long.
+//	produces a whole number of lines of output - without the trailing '\n'
+void print_int_array( int maxw, int nel, int *results, char sep, FILE *out )
+{
+	int linelen = 0;
+	for( int i=0; i<nel; i++ )
+	{
+		char buf[100];
+		sprintf( buf, "%d", results[i] );
+		int len = strlen(buf);
+		if( linelen + len + 2 > maxw )
+		{
+			fputc( '\n', out );
+			linelen = 0;
+		} else if( i>0 )
+		{
+			fputc( ' ', out );
+			linelen++;
+		}
+
+		linelen += len;
+		fprintf( out, "%s", buf );
+		if( i<nel-1 )
+		{
+			fputc( sep, out );
+			linelen++;
+		}
+	}
+	//if( linelen>0 )
+	//{
+	//	fputc( '\n', out );
+	//}
+}
diff --git a/challenge-211/duncan-c-white/C/printarray.h b/challenge-211/duncan-c-white/C/printarray.h
new file mode 100644
index 0000000000..40efb83277
--- /dev/null
+++ b/challenge-211/duncan-c-white/C/printarray.h
@@ -0,0 +1 @@
+extern void print_int_array( int maxw, int nel, int * results, char sep, FILE * out );
diff --git a/challenge-211/duncan-c-white/README b/challenge-211/duncan-c-white/README
index a7d82c8b31..a5f748da28 100644
--- a/challenge-211/duncan-c-white/README
+++ b/challenge-211/duncan-c-white/README
@@ -1,71 +1,58 @@
-Task 1: Special Bit Characters
+Task 1: Toeplitz Matrix
 
-You are given an array of binary bits that ends with 0.
-
-Valid sequences in the bit string are:
-
-[0] -decodes-to-> "a"
-[1, 0] -> "b"
-[1, 1] -> "c"
-
-Write a script to print 1 if the last character is an 'a' otherwise
-print 0.
+You are given an m x n matrix.  Write a script to find out if the given
+matrix is a Toeplitz Matrix - a matrix is Toeplitz if every diagonal
+from top-left to bottom-right has the same elements.
 
 Example 1
 
-  Input: @bits = (1, 0, 0)
-  Output: 1
-
-  The given array bits can be decoded as 2-bits character (10) followed
-  by 1-bit character (0).
+  Input: @matrix = [ [4, 3, 2, 1],
+                     [5, 4, 3, 2],
+                     [6, 5, 4, 3],
+                   ]
+  Output: true
 
 Example 2
 
-  Input: @bits = (1, 1, 1, 0)
-  Output: 0
-
-  Possible decode can be 2-bits character (11) followed by 2-bits
-  character (10) i.e. the last character is not 1-bit character.
+  Input: @matrix = [ [1, 2, 3],
+                     [3, 2, 1],
+                   ]
+  Output: false
 
-MY NOTES: very easy.  decode string then check last letter of decoded version.
-I wonder if there's a way of decoding-and-checking together, though.
+MY NOTES: sounds very easy.
 
 GUEST LANGUAGE: As a bonus, I also had a go at translating ch-1.pl into C
 (look in the C directory for that).
 
 
-Task 2: Merge Account
+Task 2: Split Same Average
 
-You are given an array of accounts i.e. name with list of email addresses.
-
-Write a script to merge the accounts where possible. The accounts can
-only be merged if they have at least one email address in common.
+You are given an array of integers.  Write a script to find out if the
+given can be split into two separate arrays whose average are the same.
 
 Example 1:
 
-  Input: @accounts = [ ["A", "a1@a.com", "a2@a.com"],
-                       ["B", "b1@b.com"],
-                       ["A", "a3@a.com", "a1@a.com"] ]
-                     ]
+  Input: @nums = (1, 2, 3, 4, 5, 6, 7, 8)
+  Output: true
 
-  Output: [ ["A", "a1@a.com", "a2@a.com", "a3@a.com"],
-            ["B", "b1@b.com"] ]
+  We can split the given array into (1, 4, 5, 8) and (2, 3, 6, 7).
+  The average of the two arrays are the same i.e. 4.5.
 
 Example 2:
 
-  Input: @accounts = [ ["A", "a1@a.com", "a2@a.com"],
-                       ["B", "b1@b.com"],
-                       ["A", "a3@a.com"],
-                       ["B", "b2@b.com", "b1@b.com"] ]
-
-  Output: [ ["A", "a1@a.com", "a2@a.com"],
-            ["A", "a3@a.com"],
-            ["B", "b1@b.com", "b2@b.com"] ]
-
-MY NOTES: fiddly and rather inelegant, especially only being allowed to
-merge two entries if the intersection of the email lists is non empty.
-Will also need to choose an input format, how about a list of words of the
-form A:a1@a.com,a2@a.com, B:b1@b.com, A:a3@a.com and B:b2@b.com,b1@b.com
-
-(TODO) GUEST LANGUAGE: As a bonus, I also had a go at translating ch-2.pl into C
-(TODO) (look in the C directory for that)
+  Input: @list = (1, 3)
+  Output: false
+
+MY NOTES: sounds easy enough as a brute force search.
+First observation: the "average of each sub-array" (our goal) must be
+the overall average, as that's the only way the sub-array averages can be
+the same value.
+Second observation: each element is either in the first subarray or in the
+second subarray, a binary counting approach is the obvious brute force method.
+(Note: I last did this in challenge 136, task 2, when we were summing subsets
+of Fibonacci numbers, so I've reused a little code from there).
+Third observation: we need only check one of the two sub-arrays (eg the first)
+as having the right sub-array average - the overall average.
+
+GUEST LANGUAGE: As a bonus, I also had a go at translating ch-2.pl into C
+(look in the C directory for that)
diff --git a/challenge-211/duncan-c-white/perl/ch-1.pl b/challenge-211/duncan-c-white/perl/ch-1.pl
new file mode 100755
index 0000000000..46284c921c
--- /dev/null
+++ b/challenge-211/duncan-c-white/perl/ch-1.pl
@@ -0,0 +1,87 @@
+#!/usr/bin/perl
+# 
+# Task 1: Toeplitz Matrix
+# 
+# You are given an m x n matrix.  Write a script to find out if the given
+# matrix is a Toeplitz Matrix - a matrix is Toeplitz if every diagonal
+# from top-left to bottom-right has the same elements.
+# 
+# Example 1
+# 
+#   Input: @matrix = [ [4, 3, 2, 1],
+#                      [5, 4, 3, 2],
+#                      [6, 5, 4, 3],
+#                    ]
+#   Output: true
+# 
+# Example 2
+# 
+#   Input: @matrix = [ [1, 2, 3],
+#                      [3, 2, 1],
+#                    ]
+#   Output: false
+# 
+# MY NOTES: sounds very easy.
+# 
+# GUEST LANGUAGE: As a bonus, I also had a go at translating ch-1.pl into C
+# (look in the C directory for that).
+# 
+
+use strict;
+use warnings;
+use feature 'say';
+use Getopt::Long;
+use Data::Dumper;
+use List::Util qw(any);
+
+my $debug=0;
+die "Usage: toeplitz [--debug] list-of-rows\n"
+	unless GetOptions( "debug"=>\$debug ) && @ARGV>0;
+
+my @m = map { [ split( /,/, $_ ) ] } @ARGV;
+
+#
+# my $same = samediag($r,$c,$rows,$cols,$mref);
+#	Return 1 iff all matrix cells in @$mref down the
+#	top-left->bottom-right diagonal starting at ($r,$c)
+#	are the same value; 0 otherwise.
+#
+sub samediag
+{
+	my( $r, $c, $rows, $cols, $mref ) = @_;
+	for( my $v = $mref->[$r][$c]; $r<$rows && $c<$cols; $r++, $c++ )
+	{
+		return 0 unless $mref->[$r][$c] == $v;