Initial data commit

Task/Knuths-algorithm-S/C/knuths-algorithm-s.c

@@ -0,0 +1,72 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+
+struct s_env {
+    unsigned int n, i;
+    size_t size;
+    void *sample;
+};
+
+void s_of_n_init(struct s_env *s_env, size_t size, unsigned int n)
+{
+    s_env->i = 0;
+    s_env->n = n;
+    s_env->size = size;
+    s_env->sample = malloc(n * size);
+}
+
+void sample_set_i(struct s_env *s_env, unsigned int i, void *item)
+{
+    memcpy(s_env->sample + i * s_env->size, item, s_env->size);
+}
+
+void *s_of_n(struct s_env *s_env, void *item)
+{
+    s_env->i++;
+    if (s_env->i <= s_env->n)
+        sample_set_i(s_env, s_env->i - 1, item);
+    else if ((rand() % s_env->i) < s_env->n)
+        sample_set_i(s_env, rand() % s_env->n, item);
+    return s_env->sample;
+}
+
+int *test(unsigned int n, int *items_set, unsigned int num_items)
+{
+    int i;
+    struct s_env s_env;
+    s_of_n_init(&s_env, sizeof(items_set[0]), n);
+    for (i = 0; i < num_items; i++) {
+        s_of_n(&s_env, (void *) &items_set[i]);
+    }
+    return (int *)s_env.sample;
+}
+
+int main()
+{
+    unsigned int i, j;
+    unsigned int n = 3;
+    unsigned int num_items = 10;
+    unsigned int *frequencies;
+    int *items_set;
+    srand(time(NULL));
+    items_set = malloc(num_items * sizeof(int));
+    frequencies = malloc(num_items * sizeof(int));
+    for (i = 0; i < num_items; i++) {
+        items_set[i] = i;
+        frequencies[i] = 0;
+    }
+    for (i = 0; i < 100000; i++) {
+        int *res = test(n, items_set, num_items);
+        for (j = 0; j < n; j++) {
+            frequencies[res[j]]++;
+        }
+	free(res);
+    }
+    for (i = 0; i < num_items; i++) {
+        printf(" %d", frequencies[i]);
+    }
+    puts("");
+    return 0;
+}