Time: 10 ms (26.92%), Space: 6.7 MB (23.85%) - LeetHub

78-subsets/78-subsets.c

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+/**
+ * Return an array of arrays of size *returnSize.
+ * The sizes of the arrays are returned as *returnColumnSizes array.
+ * Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
+ */
+int** subsets(int* nums, int numsSize, int* returnSize, int** returnColumnSizes){
+    int twoN = pow(2, numsSize);
+    int **subsets = malloc(twoN * sizeof(int *));
+    *returnColumnSizes = malloc(twoN * sizeof(int));
+    for (int i = 0; i < twoN; ++i) {
+        int iCount = i;
+        int *array = NULL;
+        int arraySize = 0;
+        int j = 0;
+        while (iCount > 0) {
+            if (iCount & 1) {
+                ++arraySize;
+                array = realloc(array, arraySize * sizeof(int));
+                array[arraySize - 1] = nums[j];
+            }
+            
+            iCount >>= 1;
+            ++j;
+        }
+        subsets[i] = array;
+        (*returnColumnSizes)[i] = arraySize;
+    }
+    *returnSize = twoN;
+    return subsets;
+}