DIY: Max Area of an Island

Problem statement

Given an m x n binary matrix grid containing 0s and 1s, you have to return the maximum contiguous area that is occupied by an island.

Each cell in the grid represents either land or water. A cell with 1 represents land, while a cell with 0 represents water. A bunch of four-directionally adjacent cells with the value 1 constitutes an island.

The area of an island is the number of cells with a value 1 in the island.

Note: You may assume that all four edges of the grid are surrounded by water.