Merge pull request #7274 from dcw803/master

added my solutions to this week's 2 tasks, both nice and easy,

13 files changed, 839 insertions, 47 deletions

diff --git a/challenge-195/duncan-c-white/C/Makefile b/challenge-195/duncan-c-white/C/Makefile
new file mode 100644
index 0000000000..34d8a4d520
--- /dev/null
+++ b/challenge-195/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
+ch-1.o:	ch-1.c args.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-195/duncan-c-white/C/README b/challenge-195/duncan-c-white/C/README
new file mode 100644
index 0000000000..5f960417f8
--- /dev/null
+++ b/challenge-195/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 even debugging)
+output to the Perl originals.
+
+They use several 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-195/duncan-c-white/C/args.c b/challenge-195/duncan-c-white/C/args.c
new file mode 100644
index 0000000000..d4a2d38b9a
--- /dev/null
+++ b/challenge-195/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-195/duncan-c-white/C/args.h b/challenge-195/duncan-c-white/C/args.h
new file mode 100644
index 0000000000..8844a8f9c4
--- /dev/null
+++ b/challenge-195/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-195/duncan-c-white/C/ch-1.c b/challenge-195/duncan-c-white/C/ch-1.c
new file mode 100644
index 0000000000..bb77b94f55
--- /dev/null
+++ b/challenge-195/duncan-c-white/C/ch-1.c
@@ -0,0 +1,69 @@
+//
+// Task 1: Special Integers
+// 
+// C version.
+// 
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+
+#include "args.h"
+
+
+//
+// bool isspecial = special( x );
+//	Return 1 iff x is special; 0 otherwise.
+//
+bool special( int x )
+{
+	int freq[10];
+
+	for( int i=0; i<10; i++ ) freq[i]=0;
+
+	// foreach digit in x
+	for( ; x>0; x/=10 )
+	{
+		int digit = x%10;
+		if( freq[digit] > 0 ) return false;
+		freq[digit]++;
+	}
+	return true;
+}
+
+
+int main( int argc, char **argv )
+{
+	int argno = process_flag_n_args( "special-numbers", argc, argv, 1, "" );
+	char *arg = argv[argno];
+	int n = atoi(arg);
+
+	if( debug )
+	{
+		printf( "debug: arg=%s, n=%d\n", arg, n );
+	}
+
+	if( n < 1 )
+	{
+		fprintf( stderr, "special-numbers: n %d must be > 0\n", n );
+		exit(1);
+	}
+
+	int nspec = 0;
+	for( int i=1; i<=n; i++ )
+	{
+		if( special(i) )
+		{
+			nspec++;
+		} else if( debug )
+		{
+			printf( "debug: %d is not special\n", i );
+		}
+	}
+	printf( "%d\n", nspec );
+
+	return 0;
+}
diff --git a/challenge-195/duncan-c-white/C/ch-2.c b/challenge-195/duncan-c-white/C/ch-2.c
new file mode 100644
index 0000000000..8e8d1a25d4
--- /dev/null
+++ b/challenge-195/duncan-c-white/C/ch-2.c
@@ -0,0 +1,189 @@
+//
+// Task 2: Most Frequent Even
+// 
+// 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"
+
+
+// This time we'll simulate a frequency hash by a list of pairs:
+// values x and their frequencies' freq
+
+typedef struct
+{
+	int x, freq;
+} pair;
+
+
+// int npairs;
+// pair *freq = make_freqs( list, nel, &npairs );
+//	Given a list of integers (and the number of elements nel)
+//	make and return a dynarray of npairs pairs of distinct
+//	elements and there frequencies
+//
+pair *make_freqs( int *list, int nel, int *npairs )
+{
+	pair *result = malloc( nel * sizeof(pair) );
+	assert( result );
+
+	*npairs = 0;
+
+	for( int i=0; i<nel; i++ )
+	{
+		bool done = false;
+		for( int p=0; p<*npairs && !done; p++ )
+		{
+			if( ! done && list[i] == result[p].x )
+			{
+				result[p].freq++;
+				done = true;
+			}
+		}
+		if( ! done )
+		{
+			int p = (*npairs)++;
+			result[p].x = list[i];
+			result[p].freq = 1;
+		}
+	}
+
+	return result;
+}
+
+
+static int compn(const void *p1, const void *p2)
+{
+   // The actual arguments to this function are "pointers to ints"
+   return (*(int *) p1) - (*(int *) p2);
+}
+
+
+//
+// int mfe = mfe( list, nel );
+//	Find and return the most-frequent-even number in list[0..nel-1],
+//	as documented above.
+//
+int mfe( int *list, int nel )
+{
+	// discard odd elements (in place)
+	for( int i=0; i<nel; i++ )
+	{
+		while( i<nel && list[i]%2 == 1 )	// odd
+		{
+			nel--;
+			if( i < nel ) list[i] = list[nel];
+		}
+	}
+
+	if( debug )
+	{
+		printf( "debug: even list: nel=%d, list= ", nel );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	if( nel==0 ) return -1;
+
+	int npairs;
+	pair *freq = make_freqs( list, nel, &npairs );
+
+	if( debug )
+	{
+		for( int i=0; i<npairs; i++ )
+		{
+			printf( "debug: f[%d] = %d\n", freq[i].x, freq[i].freq );
+		}
+	}
+
+	// find max freq
+	int maxfreq = 0;
+	for( int i=0; i<npairs; i++ )
+	{
+		if( freq[i].freq > maxfreq )
+		{
+			maxfreq = freq[i].freq;
+		}
+	}
+
+	if( debug )
+	{
+		printf( "debug, maxfreq=%d\n", maxfreq );
+	}
+
+	// find elements with max freq
+	int nm = 0;
+	int *maxf = malloc( npairs * sizeof(int) );
+	assert( maxf );
+
+	for( int i=0; i<npairs; i++ )
+	{
+		if( freq[i].freq == maxfreq )
+		{
+			maxf[nm++] = freq[i].x;
+		}
+	}
+
+	if( debug )
+	{
+		for( int i=0; i<nm; i++ )
+		{
+			printf( "debug: mf[%d] = %d\n", i, maxf[i] );
+		}
+	}
+
+	// sort the values with maximum frequencies
+	qsort( maxf, nm, sizeof(int), &compn );
+
+	if( debug )
+	{
+		printf( "debug: sorted mf[0] = %d\n", maxf[0] );
+	}
+
+	int result = maxf[0];
+
+	free( maxf );
+	free( freq );
+
+	return result;
+}
+
+
+int main( int argc, char **argv )
+{
+	int argno = process_flag_n_m_args( "most-freq-even", argc, argv,
+		1, 1000, "intlist" );
+
+	int nel;
+	int *list = parse_int_args( argc, argv, argno, &nel );
+
+	if( nel < 2 )
+	{
+		fprintf( stderr, "most-freq-even: need a list of > 1 elements\n" );
+		exit(1);
+	}
+
+	if( debug )
+	{
+		printf( "debug: initial list: " );
+		print_int_array( 60, nel, list, ',', stdout );
+		putchar( '\n' );
+	}
+
+	int result = mfe( list, nel );
+
+	printf( "%d\n", result );
+
+	free( list );
+
+	return 0;
+}
diff --git a/challenge-195/duncan-c-white/C/parseints.c b/challenge-195/duncan-c-white/C/parseints.c
new file mode 100644
index 0000000000..0fb9985633
--- /dev/null
+++ b/challenge-195/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-195/duncan-c-white/C/parseints.h b/challenge-195/duncan-c-white/C/parseints.h
new file mode 100644
index 0000000000..da5e145a86
--- /dev/null
+++ b/challenge-195/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-195/duncan-c-white/C/printarray.c b/challenge-195/duncan-c-white/C/printarray.c
new file mode 100644
index 0000000000..ddee597df3
--- /dev/null
+++ b/challenge-195/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-195/duncan-c-white/C/printarray.h b/challenge-195/duncan-c-white/C/printarray.h
new file mode 100644
index 0000000000..40efb83277
--- /dev/null
+++ b/challenge-195/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-195/duncan-c-white/README b/challenge-195/duncan-c-white/README
index f9faa0e5de..63318ee3fc 100644
--- a/challenge-195/duncan-c-white/README
+++ b/challenge-195/duncan-c-white/README
@@ -1,71 +1,50 @@
-Task 1: Digital Clock
+Task 1: Special Integers
 
-You are given time in the format hh:mm with one missing digit.
+You are given a positive integer, $n > 0.
 
-Write a script to find the highest digit between 0-9 that makes it valid time.
+Write a script to print the count of all special integers between 1 and $n:
+An integer is special when all of its digits are unique.
 
-Example 1
-
-Input: $time = '?5:00'
-Output: 1
-
-Since 05:00 and 15:00 are valid time and no other digits can fit in the
-missing place.
-
-Example 2
-
-Input: $time = '?3:00'
-Output: 2
-
-Example 3
-
-Input: $time = '1?:00'
-Output: 9
-
-Example 4
-
-Input: $time = '2?:00'
-Output: 3
-
-Example 5
+Example 1:
 
-Input: $time = '12:?5'
-Output: 5
+Input: $n = 15
+Output: 14 as except 11 all other integers between 1 and 15 are spcial.
 
-Example 6
+Example 2:
 
-Input: $time =  '12:5?'
-Output: 9
+Input: $n = 35
+Output: 32 as except 11, 22, 33 all others are special.
 
-MY NOTES: very easy
+MY NOTES: very easy; use a freq hash
 
 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: Frequency Equalizer
+Task 2: Most Frequent Even
 
-You are given a string made of alphabetic characters only, a-z.
+You are given a list of numbers, @list.
 
-Write a script to determine whether removing only one character can make
-the frequency of the remaining characters the same.
+Write a script to find most frequent even numbers in the list. In case you
+get more than one even numbers then return the smallest even integer. For
+all other case, return -1.
 
-Example 1:
+Example 1
 
-Input: $s = 'abbc'
-Output: 1 since removing one alphabet 'b' will give us 'abc' where each alphabet frequency is the same.
+Input: @list = (1,1,2,6,2)
+Output: 2 as there are only 2 even numbers 2 and 6 and of those 2 appears the most.
 
-Example 2:
+Example 2
 
-Input: $s = 'xyzyyxz'
-Output: 1 since removing 'y' will give us 'xzyyxz'.
+Input: @list = (1,3,5,7)
+Output: -1 since no even numbers found in the list
 
-Example 3:
+Example 3
 
-Input: $s = 'xzxz'
-Output: 0 since removing any one alphabet would not give us string with same frequency alphabet.
+Input: @list = (6,4,4,6,1)
+Output: 4 since there are only two even numbers 4 and 6. They both appears the equal number of times, so pick the smallest.
 
-MY NOTES: sounds pretty easy.
+MY NOTES: very easy; select even numbers; build a freq hash, sort by freqs..
 
 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)
diff --git a/challenge-195/duncan-c-white/perl/ch-1.pl b/challenge-195/duncan-c-white/perl/ch-1.pl
new file mode 100755
index 0000000000..ea2cf84f9d
--- /dev/null
+++ b/challenge-195/duncan-c-white/perl/ch-1.pl
@@ -0,0 +1,71 @@
+#!/usr/bin/perl
+# 
+# Task 1: Special Integers
+# 
+# You are given a positive integer, $n > 0.
+# 
+# Write a script to print the count of all special integers between 1 and $n:
+# An integer is special when all of its digits are unique.
+# 
+# Example 1:
+# 
+# Input: $n = 15
+# Output: 14 as except 11 all other integers between 1 and 15 are spcial.
+# 
+# Example 2:
+# 
+# Input: $n = 35
+# Output: 32 as except 11, 22, 33 all others are special.
+# 
+# MY NOTES: very easy; use a freq hash
+# 
+# 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: special-integers [--debug] N>0\n"
+	unless GetOptions( "debug"=>\$debug ) && @ARGV==1;
+
+=pod
+
+=head2 my $isspecial = special( $x );
+
+Return 1 iff $x is special; 0 otherwise.
+
+=cut
+sub special
+{
+	my( $x ) = @_;
+	my %freq;
+	foreach my $digit (split(//, $x))
+	{
+		return 0 if ++$freq{$digit}>1;
+	}
+	return 1;
+}
+
+
+
+my $n = shift;
+
+die "special-integers: n $n should be > 0\n" if $n<0;
+
+my $nspec = 0;
+foreach my $i (1..$n)
+{
+	if( special($i) )
+	{
+		$nspec++;
+	} elsif( $debug )
+	{
+		say "debug: $i is not special";
+	}
+}
+say $nspec;
diff --git a/challenge-195/duncan-c-white/perl/ch-2.pl b/challenge-195/duncan-c-white/perl/ch-2.pl
new file mode 100755
index 0000000000..450174b377
--- /dev/null
+++ b/challenge-195/duncan-c-white/perl/ch-2.pl
@@ -0,0 +1,84 @@
+#!/usr/bin/perl
+# 
+# Task 2: Most Frequent Even
+# 
+# You are given a list of numbers, @list.
+# 
+# Write a script to find most frequent even numbers in the list. In case you
+# get more than one even numbers then return the smallest even integer. For
+# all other case, return -1.
+# 
+# Example 1
+# 
+# Input: @list = (1,1,2,6,2)
+# Output: 2 as there are only 2 even numbers 2 and 6 and of those 2 appears
+# the most.
+# 
+# Example 2
+# 
+# Input: @list = (1,3,5,7)
+# Output: -1 since no even numbers found in the list
+# 
+# Example 3
+# 
+# Input: @list = (6,4,4,6,1)
+# Output: 4 since there are only two even numbers 4 and 6. They both
+# appear the equal number of times, so pick the smallest.
+# 
+# MY NOTES: very easy; select even numbers; build a freq hash, sort by freqs..
+# 
+# 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)
+# 
+
+use strict;
+use warnings;
+use feature 'say';
+use Getopt::Long;
+use List::Util qw(max);
+use Function::Parameters;
+use Data::Dumper;
+
+
+my $debug=0;
+die "Usage: most-freq-even [--debug] list(int)\n"
+	unless GetOptions( "debug"=>\$debug ) && @ARGV>1;
+
+my @list = split( /,/, join( ',', @ARGV ) );
+
+=pod
+
+=head2 my $mfe = mfe( @list );
+
+Find and return the most-frequent-even number in @list,
+as documented above.
+
+=cut
+fun mfe( @list )
+{
+	# discard odd
+	@list = grep { $_ % 2 == 0 } @list;
+
+	return -1 unless @list;
+
+	# build freq hash
+	my %freq;
+	map { $freq{$_}++ } @list;
+
+	# find max freq
+	my $max = max( values %freq );
+
+	# find elements with max freq
+	@list = grep { $freq{$_} == $max } keys %freq;
+
+	# sort them numerically, so the smallest value comes first
+	@list = sort { $a <=> $b } @list;
+
+	#die Dumper(\@list);
+
+	# that's our answer
+	return $list[0];
+}
+
+my $mfe = mfe( @list );
+say $mfe;