Solve island and frequency problems

##### Question LeetCode 200. Number of Islands – given a 2D grid, count the number of connected islands of '1's using DFS/BFS/Union-Find. LeetCode 695. Max Area of Island – return the area of the largest island (connected region of 1’s) in the grid. LeetCode 347. Top K Frequent Elements – return the k most frequent elements in an integer array using a heap / bucket sort. https://leetcode.com/problems/number-of-islands/description/ https://leetcode.com/problems/max-area-of-island/description/ https://leetcode.com/problems/top-k-frequent-elements/description/