Compute island size in grid

Given an m x n binary matrix grid of 0s (water) and 1s (land), where an island is a group of 1s connected 4-directionally, implement sizeOfIsland(grid, r, c) that returns the number of cells in the island containing cell (r, c); return 0 if (r, c) is water or out of bounds. You may either mutate grid (e.g., marking visited) or use an auxiliary visited structure—explain your choice. Describe the algorithm (DFS or BFS), clearly state the base cases, and analyze time and space complexity. Follow-up: adapt your solution to compute the size of the largest island in the entire grid.