Combinations

Signed-off-by: begeekmyfriend <[email protected]>

077_combinations/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test combinations.c

077_combinations/combinations.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+static void recursive(int n, int k, int start, int *stack, int len, bool *used,
+                      int *col_sizes, int **results, int *count)
+{
+    int i;
+    if (len == k) {
+        col_sizes[*count] = k;
+        results[*count] = malloc(k * sizeof(int));
+        memcpy(results[*count], stack, k * sizeof(int));
+        (*count)++;
+    } else {
+        for (i = start; i <= n; i++) {
+            if (!used[i]) {
+                stack[len] = i;
+                used[i] = true;
+                recursive(n, k, i + 1, stack, len + 1, used, col_sizes, results, count);
+                used[i] = false;
+            }
+        }
+    }
+}
+
+/**
+ * Return an array of arrays of size *returnSize.
+ * The sizes of the arrays are returned as *columnSizes array.
+ * Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
+ */
+int** combine(int n, int k, int** columnSizes, int* returnSize) {
+    int capacity = 10000;
+    int count = 0;
+    int **results = malloc(capacity * sizeof(int *));
+    int *stack = malloc(k * sizeof(int));
+    bool *used = malloc((n + 1) * sizeof(bool));
+    memset(used, false, n + 1);
+    *columnSizes = malloc(capacity * sizeof(int));
+    recursive(n, k, 1, stack, 0, used, *columnSizes, results, &count);
+    *returnSize = count;
+    return results;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 3) {
+        fprintf(stderr, "Usage: ./test n k\n");
+        exit(-1);
+    }
+
+    int i, j, *col_sizes, count = 0;
+    int **lists = combine(atoi(argv[1]), atoi(argv[2]), &col_sizes, &count);
+    for (i = 0; i < count; i++) {
+        for (j = 0; j < col_sizes[i]; j++) {
+            printf("%d ", lists[i][j]);
+        }
+        printf("\n");
+    }
+    return 0;
+}