1 files changed, 114 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/permute1.c b/reference/C/CONTRIB/SNIP/permute1.c
new file mode 100755
index 0000000..091ffa1
--- /dev/null
+++ b/reference/C/CONTRIB/SNIP/permute1.c
@@ -0,0 +1,114 @@
+#include<stdio.h>
+#include<stdlib.h>
+
+/*  chouse_n ( char *strng, int length) returns a pointer to a string of   */
+/*  length characters chosen from "strng" , duplicate chars in "strng" are */
+/*  significant.  Strings are generated in lexical order.                  */
+/*  First call, call with *strng. each subsiquent call, call with NULL,    */
+/*  returns one combination. Calls after all combinations have been        */
+/*  returned return NULL.  Will return NULL for errors.                    */
+/*  not very defensive (i.e. WILL BREAK)                                   */
+
+/*  dave chapman aug '91  released to public domain                        */
+
+char *chouse_n( char *strng, int length);
+
+char *chouse_n( char *strng, int length)
+{
+      static char *str;
+      static char *curr;
+      static char *pos;       /* for each char in curr(ent string),
+                                 its pos in str                            */
+      static int  counts[256];
+      int i,j;
+
+      if (0 >= length)
+            return NULL;
+
+      if (NULL != strng)
+      {
+            str = malloc(strlen(strng)); /* first call, prep string for use */
+            curr = malloc(2 * length + 1);
+            pos = curr + length +1;
+
+            for (i = 0; i < 256; counts[i++] = 0)
+                  ;
+            for (i = 0; strng[i]; i++)
+                  counts[strng[i]]++;
+
+            for (i = 1, j = 0; i < 256; i++)
+            {
+                  if (counts[i])
+                  {
+                        str[j] = i;
+                        counts[j++] = counts[i];
+                  }
+            }
+            str[j] = '\0';      /* str is string of distinct chars in order */
+                                /* counts[] holds count of each char        */
+
+            /* take first length chars */
+
+            for (i = 0,j = 0; i < length; i++)
+            {
+                  curr[i] = str[j];
+                  pos[i] = j;
+                  if (!(--counts[j]))
+                        j++;
+            }
+            curr[i] = '\0';
+            return curr;
+      }
+      /* if called with "mississippi",5;
+         str -> "imps"
+         curr -> "iiiim"
+         counts -> 0,0,2,4;
+         pos -> 0,0,0,0,1;   */
+      
+      /* go back to front */
+
+      for (j = length; j > 0;)
+      {
+            counts[ pos[--j]]++;                      /* "replace" char */
+
+            /* look for a new char for curr posit. */
+
+            for ( i = ++pos[j]; str[i] && ! counts[i]; i++)
+			;
+            if (0 != (curr[j] = str[i]))              /* found a char   */
+            {
+                  --counts[i];
+                  pos[j] = i;
+
+                  /* placed char, fill out rest of string  */
+
+                  for (++j, i = 0; j < length; j++)
+                  {
+                        for ( ; !counts[i]; i++)
+                              ;
+                        curr[j] = str[i];       /* first available char */
+                        --counts[i];
+                        pos[j] = i;
+                  }
+                  return curr;
+            }
+            /* no more chars for this pos ; go back one */
+      }
+      /*  done */
+      return NULL;
+}
+
+void main(void)
+{
+      char  *str = "aabbccdd";
+      int i,j;
+
+      j = 0;
+      i =  5;
+      puts(chouse_n( str, i));
+      while (NULL != (str = chouse_n(NULL, i)))
+      {
+            ++j;
+            printf(" %s  %d\n",str,j);
+      }
+}