Merge pull request #7674 from dcw803/master

catchup commit: challenge 205, both tasks, Perl and C, plus challenge 206: both in perl only…

17 files changed, 955 insertions, 87 deletions

diff --git a/challenge-205/duncan-c-white/C/Makefile b/challenge-205/duncan-c-white/C/Makefile
new file mode 100644
index 0000000000..1b34ccd3b2
--- /dev/null
+++ b/challenge-205/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-205/duncan-c-white/C/README b/challenge-205/duncan-c-white/C/README
new file mode 100644
index 0000000000..79d015ffe4
--- /dev/null
+++ b/challenge-205/duncan-c-white/C/README
@@ -0,0 +1,14 @@
+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
+- an int-array printing module printarray.[ch].
diff --git a/challenge-205/duncan-c-white/C/args.c b/challenge-205/duncan-c-white/C/args.c
new file mode 100644
index 0000000000..d4a2d38b9a
--- /dev/null
+++ b/challenge-205/duncan-c-white/C/args.c
@@ -0,0 +1,207 @@
+#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 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-205/duncan-c-white/C/args.h b/challenge-205/duncan-c-white/C/args.h
new file mode 100644
index 0000000000..8844a8f9c4
--- /dev/null
+++ b/challenge-205/duncan-c-white/C/args.h
@@ -0,0 +1,11 @@
+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_unsigned_real( char * val, double * n );
diff --git a/challenge-205/duncan-c-white/C/ch-1.c b/challenge-205/duncan-c-white/C/ch-1.c
new file mode 100644
index 0000000000..145ed87de0
--- /dev/null
+++ b/challenge-205/duncan-c-white/C/ch-1.c
@@ -0,0 +1,78 @@
+//
+// Task 1: Third Highest
+// 
+// C version.
+// 
+
+#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 intcomparedesc( const void *ap, const void *bp )
+{
+	int a = *((int *)ap);
+	int b = *((int *)bp);
+	return b-a;
+}
+
+
+int main( int argc, char **argv )
+{
+	int argno = process_flag_n_m_args( "third-highest", argc, argv,
+		1, 1000, "intlist" );
+
+	int nel;
+	int *list = parse_int_args( argc, argv, argno, &nel );
+
+	if( debug )
+	{
+		printf( "debug: initial list: " );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	qsort( list, nel, sizeof(int), &intcomparedesc );
+
+	if( debug )
+	{
+		printf( "debug: sorted list: " );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	// remove duplicates
+	for( int i=0; i<nel-1; i++ )
+	{
+		if( list[i+1] == list[i] )
+		{
+			// shift i+2..end back one
+			for( int j=i+2; j<nel; j++ )
+			{
+				list[j-1] = list[j];
+			}
+			nel--;
+		}
+	}
+
+	if( debug )
+	{
+		printf( "debug: no dups list: " );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	int third = ( nel > 2 ) ? list[2] : list[0];
+	printf( "%d\n", third );
+
+	free( list );
+
+	return 0;
+}
diff --git a/challenge-205/duncan-c-white/C/ch-2.c b/challenge-205/duncan-c-white/C/ch-2.c
new file mode 100644
index 0000000000..3aa2d9a358
--- /dev/null
+++ b/challenge-205/duncan-c-white/C/ch-2.c
@@ -0,0 +1,66 @@
+//
+// Task 2: Maximum XOR
+// 
+// C version.
+// 
+
+#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 main( int argc, char **argv )
+{
+	int argno = process_flag_n_m_args( "max-xor", argc, argv,
+		1, 1000, "intlist" );
+
+	int nel;
+	int *list = parse_int_args( argc, argv, argno, &nel );
+
+	if( debug )
+	{
+		printf( "debug: initial list: " );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	int max = -1;
+	int maxa = -1;
+	int maxb = -1;
+
+	for( int i=0; i<nel-1; i++ )
+	{
+		for( int j=i+1; j<nel; j++ )
+		{
+			int a = list[i]+0;
+			int b = list[j]+0;
+			int xor = a^b;
+			//say "debug: i=$i, j=$j, a=$a, b=$b, xor=$xor, max=$max" if $debug;
+			if( xor > max )
+			{
+				max = xor;
+				maxa = a;
+				maxb = b;
+			}
+		}
+	}
+
+	printf( "%d\n", max );
+
+	if( debug )
+	{
+		printf( "The maximum result of %d xor %d = %d\n",
+			maxa, maxb, max );
+	}
+
+	free( list );
+
+	return 0;
+}
diff --git a/challenge-205/duncan-c-white/C/parseints.c b/challenge-205/duncan-c-white/C/parseints.c
new file mode 100644
index 0000000000..0fb9985633
--- /dev/null
+++ b/challenge-205/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 );
+	}
+	#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_unsigned_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 );
+	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-205/duncan-c-white/C/parseints.h b/challenge-205/duncan-c-white/C/parseints.h
new file mode 100644
index 0000000000..da5e145a86
--- /dev/null
+++ b/challenge-205/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-205/duncan-c-white/C/printarray.c b/challenge-205/duncan-c-white/C/printarray.c
new file mode 100644
index 0000000000..ddee597df3
--- /dev/null
+++ b/challenge-205/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-205/duncan-c-white/C/printarray.h b/challenge-205/duncan-c-white/C/printarray.h
new file mode 100644
index 0000000000..40efb83277
--- /dev/null
+++ b/challenge-205/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-205/duncan-c-white/README b/challenge-205/duncan-c-white/README
index f38be3a4b5..3da46a12e7 100644
--- a/challenge-205/duncan-c-white/README
+++ b/challenge-205/duncan-c-white/README
@@ -1,71 +1,70 @@
-Task 1: Monotonic Array
+Task 1: Third Highest
 
 You are given an array of integers.
 
-Write a script to find out if the given array is Monotonic. Print 1 if
-it is otherwise 0.
-
-An array is Monotonic if it is either monotone increasing or decreasing.
-
-Monotone increasing: for i <= j , nums[i] <= nums[j]
-Monotone decreasing: for i <= j , nums[i] >= nums[j]
+Write a script to find out the Third Highest if found otherwise return
+the maximum.
 
 Example 1
 
-  Input: @nums = (1,2,2,3)
-  Output: 1
+  Input: @array = (5,3,4)
+  Output: 3
+
+  First highest is 5.
+  Second highest is 4.
+  Third highest is 3.
 
 Example 2
 
-  Input: @nums = (1,3,2)
-  Output: 0
+  Input: @array = (5,6)
+  Output: 6
+
+  First highest is 6.
+  Second highest is 5.
+  Third highest is missing, so maximum is returned.
 
 Example 3
 
-  Input: @nums = (6,5,5,4)
-  Output: 1
+  Input: @array = (5,4,4,3)
+  Output: 3
 
-MY NOTES: seems very easy. use reverse() in order not to detect
-monotonically increasing and decreasing..
+  First highest is 5. Second highest is 4. Third highest is 3.
+
+MY NOTES: seems very easy.  sort, take 3rd biggest distinct element
+(or biggest element if less than 3)
 
 GUEST LANGUAGE: As a bonus, I also had a go at translating ch-1.pl
 into C (look in the C directory for the translation)
 
 
-Task 2: Reshape Matrix
-
-You are given a matrix (m x n) and two integers (r) and (c).
+Task 2: Maximum XOR
 
-Write a script to reshape the given matrix in form (r x c) with the
-original value in the given matrix. If you can't reshape print 0.
+You are given an array of integers.
+Write a script to find the highest value obtained by XORing any two
+distinct members of the array.
 
 Example 1
 
-Input: $matrix = [ [ 1, 2 ], [ 3, 4 ] ]
-       $r = 1
-       $c = 4
+  Input: @array = (1,2,3,4,5,6,7)
+  Output: 7
 
-Output: [ 1 2 3 4 ]
+  The maximum result of 1 xor 6 = 7.
 
 Example 2
 
-Input: $matrix = [ [ 1, 2, 3 ] , [ 4, 5, 6 ] ]
-       $r = 3
-       $c = 2
+  Input: @array = (2,4,1,3)
+  Output: 7
 
-Output: [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ]
+  The maximum result of 4 xor 3 = 7.
 
 Example 3
 
-Input: $matrix = [ [ 1, 2 ] ]
-       $r = 3
-       $c = 2
+  Input: @array = (10,5,7,12,8)
+  Output: 15
 
-Output: 0
+  The maximum result of 10 xor 5 = 15.
 
-MY NOTES: also quite easy, can be done if R1*C1==R2*C
-(of course we have to discover R1 and C1, the dimensions o
-the original matrix).  Also have to read the matrix in..
+MY NOTES: also quite easy, try all combinations, pick max of all xors.
 
 GUEST LANGUAGE: As a bonus, I also had a go at translating ch-2.pl
 into C (look in the C directory for the translation).  Needed to
diff --git a/challenge-205/duncan-c-white/perl/ch-1.pl b/challenge-205/duncan-c-white/perl/ch-1.pl
new file mode 100755
index 0000000000..ee3dec3163
--- /dev/null
+++ b/challenge-205/duncan-c-white/perl/ch-1.pl
@@ -0,0 +1,65 @@
+#!/usr/bin/perl
+# 
+# Task 1: Third Highest
+# 
+# You are given an array of integers.
+# 
+# Write a script to find out the Third Highest if found otherwise return
+# the maximum.
+# 
+# Example 1
+# 
+#   Input: @array = (5,3,4)
+#   Output: 3
+# 
+#   First highest is 5.
+#   Second highest is 4.
+#   Third highest is 3.
+# 
+# Example 2
+# 
+#   Input: @array = (5,6)
+#   Output: 6
+# 
+#   First highest is 6.
+#   Second highest is 5.
+#   Third highest is missing, so maximum is returned.
+# 
+# Example 3
+# 
+#   Input: @array = (5,4,4,3)
+#   Output: 3
+# 
+#   First highest is 5. Second highest is 4. Third highest is 3.
+# 
+# MY NOTES: seems very easy.  sort, take 3rd biggest distinct element
+# (or biggest element if less than 3)
+# 
+# GUEST LANGUAGE: As a bonus, I also had a go at translating ch-1.pl
+# into C (look in the C directory for the translation)
+#
+
+use strict;
+use warnings;
+use feature 'say';
+use Getopt::Long;
+use Data::Dumper;
+
+my $debug=0;
+die "Usage: third-highest [--debug] intlist\n"
+	unless GetOptions( "debug"=>\$debug ) && @ARGV>0;
+
+my @list = split( /,/, join(',',@ARGV) );
+
+@list = sort { $b <=> $a } @list;
+
+say "sorted: ", join(',',@list) if $debug;
+
+# remove dups
+my %seen;
+@list = grep { ! $seen{$_}++ } @list;
+
+say "nodups: ", join(',',@list) if $debug;
+
+my $third = ( @list > 2 ) ? $list[2] : $list[0];
+say $third;
diff --git a/challenge-205/duncan-c-white/perl/ch-2.pl b/challenge-205/duncan-c-white/perl/ch-2.pl
new file mode 100755
index 0000000000..4a71341928
--- /dev/null
+++ b/challenge-205/duncan-c-white/perl/ch-2.pl
@@ -0,0 +1,75 @@
+#!/usr/bin/perl
+#
+# Task 2: Maximum XOR
+# 
+# You are given an array of integers.
+# Write a script to find the highest value obtained by XORing any two
+# distinct members of the array.
+# 
+# Example 1
+# 
+#   Input: @array = (1,2,3,4,5,6,7)
+#   Output: 7
+# 
+#   The maximum result of 1 xor 6 = 7.
+# 
+# Example 2
+# 
+#   Input: @array = (2,4,1,3)
+#   Output: 7
+# 
+#   The maximum result of 4 xor 3 = 7.
+# 
+# Example 3
+# 
+#   Input: @array = (10,5,7,12,8)
+#   Output: 15
+# 
+#   The maximum result of 10 xor 5 = 15.
+# 
+# MY NOTES: also quite easy, try all combinations, pick max of all xors.
+# 
+# GUEST LANGUAGE: As a bonus, I also had a go at translating ch-2.pl
+# into C (look in the C directory for the translation).  Needed to
+# pass original sizes into C routine..
+#
+
+use strict;
+use warnings;
+use feature 'say';
+use Getopt::Long;
+use Function::Parameters;
+use Data::Dumper;
+
+my $debug=0;
+die "Usage: max-xor [--debug] intlist\n"
+	unless GetOptions( "debug"=>\$debug ) && @ARGV > 0;
+
+my @list = split( /,/, join(',',@ARGV) );
+
+say "list: ", join(',',@list) if $debug;
+
+my $max = -1;
+my $maxa = -1;
+my $maxb = -1;
+
+foreach my $i (0..$#list-1)
+{
+	foreach my $j ($i+1..$#list)
+	{
+		my $a = $list[$i]+0;
+		my $b = $list[$j]+0;
+		my $xor = $a^$b;
+		#say "debug: i=$i, j=$j, a=$a, b=$b, xor=$xor, max=$max" if $debug;
+		if( $xor > $max )
+		{
+			$max = $xor;
+			$maxa = $a;
+			$maxb = $b;
+		}
+	}
+}
+
+say "$max";
+
+say "The maximum result of $maxa xor $maxb = $max" if $debug;
diff --git a/challenge-206/duncan-c-white/C/.cbuild b/challenge-206/duncan-c-white/C/.cbuild
deleted file mode 100644
index a14ec76520..0000000000
--- a/challenge-206/duncan-c-white/C/.cbuild
+++ /dev/null
@@ -1,4 +0,0 @@
-BUILD = ch-1 ch-2
-CFLAGS = -Wall -g
-#LDFLAGS = -lm
-#CFLAGS = -g
diff --git a/challenge-206/duncan-c-white/README b/challenge-206/duncan-c-white/README
index f38be3a4b5..3a95b6badb 100644
--- a/challenge-206/duncan-c-white/README
+++ b/challenge-206/duncan-c-white/README
@@ -1,72 +1,66 @@
-Task 1: Monotonic Array
+Task 1: Shortest Time
 
-You are given an array of integers.
-
-Write a script to find out if the given array is Monotonic. Print 1 if
-it is otherwise 0.
-
-An array is Monotonic if it is either monotone increasing or decreasing.
-
-Monotone increasing: for i <= j , nums[i] <= nums[j]
-Monotone decreasing: for i <= j , nums[i] >= nums[j]
+You are given a list of time points, at least 2, in the 24-hour clock
+format HH:MM.  Write a script to find out the shortest time in minutes
+between any two time points.
 
 Example 1
 
-  Input: @nums = (1,2,2,3)
-  Output: 1
+  Input: @time = ("00:00", "23:55", "20:00")
+  Output: 5
+
+  Since the difference between "00:00" and "23:55" is the shortest (5 minutes).
 
 Example 2
 
-  Input: @nums = (1,3,2)
-  Output: 0
+  Input: @array = ("01:01", "00:50", "00:57")
+  Output: 4
 
 Example 3
 
-  Input: @nums = (6,5,5,4)
-  Output: 1
-
-MY NOTES: seems very easy. use reverse() in order not to detect
-monotonically increasing and decreasing..
+  Input: @array = ("10:10", "09:30", "09:00", "09:55")
+  Output: 15
 
-GUEST LANGUAGE: As a bonus, I also had a go at translating ch-1.pl
-into C (look in the C directory for the translation)
+MY NOTES: reasonably easy, although of course wraparound has to taken
+into account.  Might convert each hh:mm time into a number of minutes,
+then sort the array.. then check every adjacant pair (including the
+wraparound pair, i.e the last and the first)..
 
+No C solutions today.  Might do them later..
 
-Task 2: Reshape Matrix
 
-You are given a matrix (m x n) and two integers (r) and (c).
+Task 2: Array Pairings
 
-Write a script to reshape the given matrix in form (r x c) with the
-original value in the given matrix. If you can't reshape print 0.
+You are given an array of integers having even number of elements..
+Write a script to find the maximum sum of the minimum of each pairs.
 
 Example 1
 
-Input: $matrix = [ [ 1, 2 ], [ 3, 4 ] ]
-       $r = 1
-       $c = 4
+  Input: @array = (1,2,3,4)
+  Output: 4
 
-Output: [ 1 2 3 4 ]
+  Possible Pairings are as below:
+  a) (1,2) and (3,4). So min(1,2) + min(3,4) => 1 + 3 => 4
+  b) (1,3) and (2,4). So min(1,3) + min(2,4) => 1 + 2 => 3
+  c) (1,4) and (2,3). So min(1,4) + min(2,3) => 2 + 1 => 3
 
-Example 2
-
-Input: $matrix = [ [ 1, 2, 3 ] , [ 4, 5, 6 ] ]
-       $r = 3
-       $c = 2
-
-Output: [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ]
+  So the maxium sum is 4.
 
-Example 3
+Example 2
 
-Input: $matrix = [ [ 1, 2 ] ]
-       $r = 3
-       $c = 2
+  Input: @array = (0,2,1,3)
+  Output: 2
 
-Output: 0
+  Possible Pairings are as below:
+  a) (0,2) and (1,3). So min(0,2) + min(1,3) => 0 + 1 => 1
+  b) (0,1) and (2,3). So min(0,1) + min(2,3) => 0 + 2 => 2
+  c) (0,3) and (2,1). So min(0,3) + min(2,1) => 0 + 1 => 1
+  
+  So the maximum sum is 2.
 
-MY NOTES: also quite easy, can be done if R1*C1==R2*C
-(of course we have to discover R1 and C1, the dimensions o
-the original matrix).  Also have to read the matrix in..
+MY NOTES: hmm. I wish one of the examples had 6 elements.  It seems
+to me that this sounds like a recursive solution..  Pick each possible
+pair involving the first element and each of the others (in turn),
+remove them, calculate and total up the minimum, then recurse.
 
-GUEST LANGUAGE: As a bonus, I also had a go at translating ch-2.pl
-into C (look in the C directory for the translation).  Needed to
-pass original sizes into C routine..
+No C solutions today.  Might do them later..
diff --git a/challenge-206/duncan-c-white/perl/ch-1.pl b/challenge-206/duncan-c-white/perl/ch-1.pl
new file mode 100755
index 0000000000..9a06b20182
--- /dev/null
+++ b/challenge-206/duncan-c-white/perl/ch-1.pl
@@ -0,0 +1,94 @@
+#!/usr/bin/perl
+# 
+# Task 1: Shortest Time
+# 
+# You are given a list of time points, at least 2, in the 24-hour clock
+# format HH:MM.  Write a script to find out the shortest time in minutes
+# between any two time points.
+# 
+# Example 1
+# 
+#   Input: @time = ("00:00", "23:55", "20:00")
+#   Output: 5
+# 
+#   Since the difference between "00:00" and "23:55" is the shortest (5 minutes).
+# 
+# Example 2
+# 
+#   Input: @array = ("01:01", "00:50", "00:57")
+#   Output: 4
+# 
+# Example 3</