From 5978cc86c5807a7fe36cba8a227c0001ecaa66d6 Mon Sep 17 00:00:00 2001
From: David Phillips <david@sighup.nz>
Date: Thu, 14 Sep 2017 20:45:22 +1200
Subject: Improve algorithm for permutations

---
 words-misc/permutations.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/words-misc/permutations.c b/words-misc/permutations.c
index 4fafde0..7f6b0ef 100644
--- a/words-misc/permutations.c
+++ b/words-misc/permutations.c
@@ -2,42 +2,42 @@
 #include <stdlib.h>
 #include <string.h>
 
-/* FIXME hacked together 6 months ago, not sure if finished */
-/* FIXME does duplicates */
-
 void swap_chr(char*, char*);
-void p(char *, size_t);
+void p(char *, size_t, size_t);
+void die_help(const char*);
 
 int main(int argc, char **argv)
 {
 	if (argc != 2)
-	{
-		fprintf(stderr, "Usage: %s <word>\n", argv[0]);
-		return EXIT_FAILURE;
-	}
+		die_help(argv[0]);
 
-	p(argv[1], 0);
+	p(argv[1], strlen(argv[1]), 0);
 
 	return 0;
 }
 
+void die_help(const char* argv0) {
+	fprintf(stderr, "Usage: %s <word>\n", argv0);
+	exit(1);
+}
+
 void swap_chr(char *a, char *b) {
 	char t = *a;
 	*a = *b;
 	*b = t;
 }
 
-void p(char *string, size_t x)
-{
-	size_t i = 0;
+void p(char *string, size_t x, size_t i) {
+	size_t j = 0;
 
-	if (x == strlen(string)) {
+	if (i == x) {
 		puts(string);
 		return;
 	}
-	for (i = 0; i < strlen(string); i++) {
-		swap_chr(&string[x], &string[i]);
-		p(string, x + 1);
-		swap_chr(&string[x], &string[i]);
+
+	for (j = i; j < x; j++) {
+		swap_chr(&string[i], &string[j]);
+		p(string, x, i+1);
+		swap_chr(&string[i], &string[j]);
 	}
 }
-- 
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