feat: add H-Index LeetCode problem (#1188)

* add leetcode H-Index

* Update leetcode/src/274.c

Co-authored-by: Taj <tjgurwara99@users.noreply.github.com>

* Update 274.c

fix review notes.

Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: Taj <tjgurwara99@users.noreply.github.com>

leetcode/DIRECTORY.md

@@ -69,6 +69,7 @@
 | 236  | [Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/)               | [C](./src/236.c)  | Medium     |
 | 242  | [Valid Anagram](https://leetcode.com/problems/valid-anagram/)                                                                   | [C](./src/242.c)  | Easy       |
 | 268  | [Missing Number](https://leetcode.com/problems/missing-number/)                                                                 | [C](./src/268.c)  | Easy       |
+| 274  | [H-Index](https://leetcode.com/problems/h-index/description/)                                                                   | [C](./src/274.c)  | Medium     |
 | 278  | [First Bad Version](https://leetcode.com/problems/first-bad-version/)                                                           | [C](./src/278.c)  | Easy       |
 | 283  | [Move Zeroes](https://leetcode.com/problems/move-zeroes/)                                                                       | [C](./src/283.c)  | Easy       |
 | 287  | [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)                                           | [C](./src/287.c)  | Medium     |

leetcode/src/274.c

@@ -0,0 +1,21 @@
+int diff(const int* i, const int* j)
+
+{
+    return *i - *j;
+}
+
+
+// Sorting.
+// Runtime: O(n*log(n))
+// Space: O(1)
+int hIndex(int* citations, int citationsSize){
+    qsort(citations, citationsSize, sizeof(int), (int(*) (const void*, const void*)) diff);
+
+    for(int i = 0; i < citationsSize; i++){
+        if (citations[citationsSize - 1 - i] <= i){
+            return i;
+        }
+    }
+
+    return citationsSize;
+}