add Two Sum task

Two Sum/solution.c

@@ -0,0 +1,48 @@
+#include <stdlib.h>
+
+typedef struct {
+    int key;
+    int value;
+    int used;
+} Entry;
+
+int hash(int key, int size) {
+    return (key % size + size) % size;
+}
+
+int* twoSum(int* nums, int numsSize, int target, int* returnSize) {
+
+    int tableSize = numsSize * 2;
+    Entry* table = calloc(tableSize, sizeof(Entry));
+
+    int* res = malloc(sizeof(int) * 2);
+    *returnSize = 2;
+
+    for (int i = 0; i < numsSize; i++) {
+        int complement = target - nums[i];
+        int h = hash(complement, tableSize);
+
+        while (table[h].used) {
+            if (table[h].key == complement) {
+                res[0] = i;
+                res[1] = table[h].value;
+                free(table);
+                return res;
+            }
+            h = (h + 1) % tableSize;
+        }
+
+        h = hash(nums[i], tableSize);
+        while (table[h].used) {
+            h = (h + 1) % tableSize;
+        }
+
+        table[h].used = 1;
+        table[h].key = nums[i];
+        table[h].value = i;
+    }
+
+    free(table);
+    return res;
+}
+