Add C solution for 78-Subsets.c

Author: th-blitz

Diff for: c/78-Subsets.c

@@ -0,0 +1,50 @@
+
+
+/**
+ * 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 nCr(int* factorials, int n, int r) {
+    return (int)(factorials[n] / (factorials[r] * (factorials[n - r])));
+}
+
+int** subsets(int* nums, int numsSize, int* returnSize, int** returnColumnSizes){
+    
+    int* factorials = (int*)malloc((numsSize + 1) * sizeof(int));
+    factorials[0] = 1;
+    factorials[1] = 1;
+    
+    for (int i = 2; i < (numsSize + 1); i++) {
+        factorials[i] = factorials[i - 1] * i;
+    }
+    
+    int combinations = 0;
+    for (int i = 0; i < (numsSize + 1); i++) {
+        combinations += nCr(factorials, numsSize, i);
+    }
+    *returnSize = combinations;
+    
+    int** result = (int**)malloc(combinations * sizeof(int*));
+    returnColumnSizes[0] = (int*)malloc(combinations * sizeof(int));
+    returnColumnSizes[0][0] = 0;
+    
+    int current_size = 1;
+    int lead = 1;
+    for (int i = 0; i < numsSize; i++) {
+        for (int j = 0; j < current_size; j++) {
+            int* new_subset = (int*)malloc((returnColumnSizes[0][j] + 1) * sizeof(int));
+            for (int k = 0; k < returnColumnSizes[0][j]; k++) {
+                new_subset[k] = result[j][k];
+            }
+            new_subset[returnColumnSizes[0][j]] = nums[i];
+            result[lead] = new_subset;
+            returnColumnSizes[0][lead] = (returnColumnSizes[0][j] + 1);  
+            lead += 1;
+        }   
+        current_size = lead;
+    }
+    free(factorials);
+    return result;
+}