feat: add Sum of Even Numbers LeetCode problem (#1145)

* add Sum of Even Numbers After Queries leetcode task

* chore: apply suggestions from code review

Co-authored-by: David Leal <halfpacho@gmail.com>

leetcode/DIRECTORY.md

@@ -92,6 +92,7 @@
 | 938  | [Range Sum of BST](https://leetcode.com/problems/range-sum-of-bst/)                                                             | [C](./src/938.c)  | Easy       |
 | 965  | [Univalued Binary Tree](https://leetcode.com/problems/univalued-binary-tree/)                                                   | [C](./src/965.c)  | Easy       |
 | 977  | [Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/)                                           | [C](./src/977.c)  | Easy       |
+| 985  | [Sum of Even Numbers After Queries](https://leetcode.com/problems/sum-of-even-numbers-after-queries/)                           | [C](./src/985.c)  | Medium     |
 | 1009 | [Complement of Base 10 Integer](https://leetcode.com/problems/complement-of-base-10-integer/)                                   | [C](./src/1009.c) | Easy       |
 | 1089 | [Duplicate Zeros](https://leetcode.com/problems/duplicate-zeros/)                                                               | [C](./src/1089.c) | Easy       |
 | 1184 | [Distance Between Bus Stops](https://leetcode.com/problems/distance-between-bus-stops/)                                         | [C](./src/1184.c) | Easy       |

leetcode/src/985.c

@@ -0,0 +1,39 @@
+/**
+ * Note: The returned array must be malloced, assume caller calls free().
+ */
+
+// collecting sum Runtime: O(len(queries)), Space: O(1)
+int* sumEvenAfterQueries(int* nums, int numsSize, int** queries, int queriesSize, int* queriesColSize, int* returnSize){
+    int summ = 0;
+    int* result = malloc(queriesSize * sizeof(int));
+    *returnSize = queriesSize;
+    
+    for(int i = 0; i < numsSize; i++){
+        if (nums[i] % 2 == 0) {
+            summ += nums[i];
+        }
+    }
+    
+    for(int i = 0; i < queriesSize; i++){
+        int* query = queries[i];
+        int val = query[0];
+        int index = query[1];
+        
+        // sub index value from summ if it's even
+        if (nums[index] % 2 == 0) {
+            summ -= nums[index];
+        }
+
+        // modify the nums[index] value
+        nums[index] += val;
+
+        // add index value from summ if it's even
+        if (nums[index] % 2 == 0) {
+            summ += nums[index];
+        }
+        
+        result[i] = summ;
+    }
+    
+    return result;
+}