From 6d3a2db228f138453c4e94d2332426cd2db28ff7 Mon Sep 17 00:00:00 2001
From: dcw <d.white@imperial.ac.uk>
Date: Mon, 5 Dec 2022 15:42:03 +0000
Subject: slight tweak to ch-2.pl and then translated it into C (see C/ch-2.c
 for that), sorting an array of pairs (strings + difference signatures) by
 signature using qsort..

---
 challenge-193/duncan-c-white/C/.cbuild    |   2 +-
 challenge-193/duncan-c-white/C/Makefile   |   4 +-
 challenge-193/duncan-c-white/C/README     |   8 +-
 challenge-193/duncan-c-white/C/ch-2.c     | 200 ++++++++++++++++++++++++++++++
 challenge-193/duncan-c-white/perl/ch-2.pl |   6 +-
 5 files changed, 209 insertions(+), 11 deletions(-)
 create mode 100644 challenge-193/duncan-c-white/C/ch-2.c

diff --git a/challenge-193/duncan-c-white/C/.cbuild b/challenge-193/duncan-c-white/C/.cbuild
index 624a95ebfb..a14ec76520 100644
--- a/challenge-193/duncan-c-white/C/.cbuild
+++ b/challenge-193/duncan-c-white/C/.cbuild
@@ -1,4 +1,4 @@
-BUILD = ch-1
+BUILD = ch-1 ch-2
 CFLAGS = -Wall -g
 #LDFLAGS = -lm
 #CFLAGS = -g
diff --git a/challenge-193/duncan-c-white/C/Makefile b/challenge-193/duncan-c-white/C/Makefile
index e9ebaeaa96..8d85c7d16d 100644
--- a/challenge-193/duncan-c-white/C/Makefile
+++ b/challenge-193/duncan-c-white/C/Makefile
@@ -1,7 +1,7 @@
 # Makefile rules generated by CB
 CC	= gcc
 CFLAGS	= -Wall -g
-BUILD	= ch-1
+BUILD	= ch-1 ch-2
 
 all:	$(BUILD)
 
@@ -11,4 +11,6 @@ clean:
 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
+ch-2.o:	ch-2.c args.h
 
diff --git a/challenge-193/duncan-c-white/C/README b/challenge-193/duncan-c-white/C/README
index 6664968152..a5adc6cda7 100644
--- a/challenge-193/duncan-c-white/C/README
+++ b/challenge-193/duncan-c-white/C/README
@@ -1,7 +1,7 @@
-Thought I'd also have a go at translating ch-1.pl into C..
+Thought I'd also have a go at translating ch-1.pl and ch-2.pl into C..
 
-It produces near-identical (non-debugging and even debugging) output to the
-Perl original.
+Both C versions produce near-identical (non-debugging and even debugging)
+output to the Perl originals.
 
-It uses one of my regular support modules:
+They use one of my regular support modules:
 - a command-line argument processing module args.[ch]
diff --git a/challenge-193/duncan-c-white/C/ch-2.c b/challenge-193/duncan-c-white/C/ch-2.c
new file mode 100644
index 0000000000..2a525f28ec
--- /dev/null
+++ b/challenge-193/duncan-c-white/C/ch-2.c
@@ -0,0 +1,200 @@
+//
+// Task 2: Odd Strings
+// 
+// C version.
+// 
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+
+#include "args.h"
+
+
+//
+// char *diffsig = diffsig(str);
+//
+// Given an alphabetic string $str, form and return the difference signature.
+// (a malloc()d string, the caller is responsible for freeing it later).
+//
+char * diffsig( char *str )
+{
+	int len = strlen(str);
+	assert( len > 1 );
+	char *result = malloc( 4 * len + 2 );	// 4 * len: optional -, 1 or 2
+						// digits and a comma:
+						// then add a bit:-)
+	assert( result != NULL );
+
+	char *rp = result;	// rp will walk the result, appending chars
+	*rp = '\0';		// let's keep it nul-terminated always
+
+	// foreach char *p that is not the last
+	for( char *p=str; *(p+1) != '\0'; p++ )
+	{
+		if( p>str ) *rp++ = ',';
+		sprintf( rp, "%d", *(p+1)-*p );
+		while( *rp != '\0' ) rp++;
+	}
+
+	//printf( "debug: diffstr(%s) = %s\n", str, result );
+	return result;
+}
+
+
+//
+// lowercase(str);
+//	lowercase str in place.
+//
+void lowercase( char *str )
+{
+	for( char *p=str; *p; p++ )
+	{
+		*p = tolower(*p);
+	}
+}
+
+
+// a (string, diffsig) pair
+typedef struct
+{
+	char *str;
+	char *sig;
+} pair;
+
+
+// qsort comparator for a pair.. couldn't resist the name..
+static int compair( const void *a, const void *b )
+{
+	pair *p = (pair *)a;
+	pair *q = (pair *)b;
+	return strcmp( p->sig, q->sig );
+}
+
+
+// a ptr to a function taking a signature and list[from]..list[to]
+// comprising all the strings with that signature.
+typedef void (*sigcallback)( char *sig, pair *list, int from, int to );
+
+
+//
+// find_freq_sigs( list, nel, cb );
+//	given a sorted list of nel pairs, locate each set of strings
+//	with distinct signatures, and call the cb function for each
+//	set found.
+//
+void find_freq_sigs( pair *list, int nel, sigcallback cb )
+{
+	char *sig = "";
+	int from = -1;
+	int to = -1;
+	for( int i=0; i<nel; i++ )
+	{
+		if( strcmp( sig, list[i].sig ) != 0 )
+		{
+			// found different signature list[i].sig
+			// deal with previous set
+			if( *sig != '\0' )
+			{
+				(*cb)( sig, list, from, to );
+			}
+
+			from = i;
+			to = i;
+			sig = list[i].sig;
+		} else
+		{
+			to++;
+		}
+	}
+	// deal with final set
+	if( *sig != '\0' )
+	{
+		(*cb)( sig, list, from, to );
+	}
+}
+
+
+static void printsigset( char *sig, pair *list, int from, int to )
+{
+	int freq = to-from+1;
+	//printf( "sig %s: list[%d]=%s..list[%d]=%s, freq %d\n",
+	//	sig, from, list[from].str, to, list[to].str, freq );
+	if( freq == 1 )
+	{
+		if( debug )
+		{
+			printf( "unique sig %s: %s\n", sig, list[from].str );
+		} else
+		{
+			printf( "%s\n", list[from].str );
+		}
+	}
+}
+
+
+int main( int argc, char **argv )
+{
+	int argno = process_flag_n_m_args( "odd-strings", argc, argv,
+		1, 100, "strlist" );
+
+	if( debug )
+	{
+		printf( "debug: argno=%d, argc=%d\n", argno, argc );
+	}
+
+	pair list[argc-argno];		// list[i-argno].str : argv[i],
+					// list[i-argno].sig : diffsig(lc(argv[i]))
+
+	// build list.. indexes 0..argc-argno-1
+	int nel=0;
+	for( int i=argno; i<argc; i++ )
+	{
+		list[nel].str = strdup(argv[i]);
+		lowercase(list[nel].str);
+		list[nel].sig = diffsig(list[nel].str);
+		if( debug )
+		{
+			printf( "debug: unsorted list[%d].str=%s, "
+			        "list[%d].sig=%s\n",
+				nel, list[nel].str,
+				nel, list[nel].sig );
+		}
+		nel++;
+	}
+
+	if( debug )
+	{
+		printf( "debug: nel=%d\n", nel );
+	}
+
+	// sort list by signature
+	qsort( list, nel, sizeof(pair), &compair );
+
+	// show sorted list
+	if( debug )
+	{
+		for( int i=0; i<nel; i++ )
+		{
+			printf( "debug: sorted list[%d].str=%s, "
+			        "list[%d].sig=%s\n",
+				i, list[i].str, i, list[i].sig );
+
+		}
+	}
+
+	if( debug ) putchar( '\n' );
+	find_freq_sigs( list, nel, &printsigset );
+
+	// tidy up.. free everything we malloc()d
+	for( int i=0; i<nel; i++ )
+	{
+		free( list[i].sig );
+		free( list[i].str );
+	}
+
+	return 0;
+}
diff --git a/challenge-193/duncan-c-white/perl/ch-2.pl b/challenge-193/duncan-c-white/perl/ch-2.pl
index 988f4819cf..4fb47aa330 100755
--- a/challenge-193/duncan-c-white/perl/ch-2.pl
+++ b/challenge-193/duncan-c-white/perl/ch-2.pl
@@ -106,11 +106,7 @@ map { $freq{$_}++ } @diffsig;
 
 foreach my $k (keys %freq)
 {
-	delete $freq{$k} if $freq{$k}>1;
-}
-
-foreach my $k (keys %freq)
-{
+	next if $freq{$k}>1;
 	my $ref = $d2l{$k};
 	say join(',', @$ref);
 }
-- 
cgit