feat: add Frequency of the Most Frequent Element (#1195)

* add leetcode Frequency of the Most Frequent Element

* Update 1838.c

small fix

* Update leetcode/src/1838.c

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

leetcode/DIRECTORY.md

@@ -118,6 +118,7 @@
 | 1524 | [Number of Sub-arrays With Odd Sum](https://leetcode.com/problems/number-of-sub-arrays-with-odd-sum/)                           | [C](./src/1524.c) | Medium     |
 | 1653 | [Minimum Deletions to Make String Balanced](https://leetcode.com/problems/minimum-deletions-to-make-string-balanced/)           | [C](./src/1653.c) | Medium     |
 | 1704 | [Determine if String Halves Are Alike](Determine if String Halves Are Alike)                                                    | [C](./src/1704.c) | Easy       |
+| 1838 | [Frequency of the Most Frequent Element](https://leetcode.com/problems/frequency-of-the-most-frequent-element/)                 | [C](./src/1838.c) | Medium     |
 | 1752 | [Check if Array Is Sorted and Rotated](https://leetcode.com/problems/check-if-array-is-sorted-and-rotated/)                     | [C](./src/1752.c) | Easy       |
 | 2024 | [Maximize the Confusion of an Exam](https://leetcode.com/problems/maximize-the-confusion-of-an-exam/)                           | [C](./src/2024.c) | Medium     |
 | 2095 | [Delete the Middle Node of a Linked List](https://leetcode.com/problems/delete-the-middle-node-of-a-linked-list/)               | [C](./src/2095.c) | Medium     |

leetcode/src/1838.c

@@ -0,0 +1,36 @@
+#define max(a,b) (((a)>(b))?(a):(b))
+
+int compare(const int* i, const int* j)
+{
+    return *i - *j;
+}
+
+// Sort + prefix sum + windows sliding
+// Runtime: O(n*log(n))
+// Space: O(n)
+int maxFrequency(int* nums, int numsSize, int k){
+    qsort(nums, numsSize, sizeof (int), (int(*) (const void*, const void*)) compare);
+    long* prefixSum = malloc(numsSize * sizeof(long));
+    
+    prefixSum[0] = nums[0];
+    for(int i = 0; i < numsSize - 1; i++){
+        prefixSum[i + 1] = prefixSum[i] + nums[i];
+    }
+
+    int leftWindowPosition = 0;
+    int result = 0;
+    
+    for(int rightWindowPosition = 0; rightWindowPosition < numsSize; rightWindowPosition++){
+        long rightSum = prefixSum[rightWindowPosition];
+        long leftSum = prefixSum[leftWindowPosition];
+
+        while ((long)nums[rightWindowPosition] * (rightWindowPosition - leftWindowPosition) - (rightSum - leftSum) > k){
+            leftWindowPosition += 1;
+        }
+
+        result = max(result, rightWindowPosition - leftWindowPosition + 1);
+    }
+
+    free(prefixSum);
+    return result;
+}