Data commit

Task/Permutations-Derangements/C/permutations-derangements.c

@@ -0,0 +1,57 @@
+#include <stdio.h>
+typedef unsigned long long LONG;
+
+LONG deranged(int depth, int len, int *d, int show)
+{
+        int i;
+        char tmp;
+        LONG count = 0;
+
+        if (depth == len) {
+                if (show) {
+                        for (i = 0; i < len; i++) putchar(d[i] + 'a');
+                        putchar('\n');
+                }
+                return 1;
+        }
+        for (i = len - 1; i >= depth; i--) {
+                if (i == d[depth]) continue;
+
+                tmp = d[i]; d[i] = d[depth]; d[depth] = tmp;
+                count += deranged(depth + 1, len, d, show);
+                tmp = d[i]; d[i] = d[depth]; d[depth] = tmp;
+        }
+        return count;
+}
+
+LONG gen_n(int n, int show)
+{
+        LONG i;
+        int a[1024]; /* 1024 ought to be big enough for anybody */
+
+        for (i = 0; i < n; i++) a[i] = i;
+        return deranged(0, n, a, show);
+}
+
+LONG sub_fact(int n)
+{
+        return n < 2 ? 1 - n : (sub_fact(n - 1) + sub_fact(n - 2)) * (n - 1);
+}
+
+int main()
+{
+        int i;
+
+        printf("Deranged Four:\n");
+        gen_n(4, 1);
+
+        printf("\nCompare list vs calc:\n");
+        for (i = 0; i < 10; i++)
+                printf("%d:\t%llu\t%llu\n", i, gen_n(i, 0), sub_fact(i));
+
+        printf("\nfurther calc:\n");
+        for (i = 10; i <= 20; i++)
+                printf("%d: %llu\n", i, sub_fact(i));
+
+        return 0;
+}