695. 岛屿的最大面积

// LeetCode指定调用方法     
public int maxAreaOfIsland(int[][] grid) {

    int maxArea = 0;
    for (int i = 0; i < grid.length; i++) {
        for (int j = 0; j < grid[0].length; j++) {

            // 值为1时进行一次DFS
            if (grid[i][j] == 1) {
                maxArea = Math.max(maxArea, dfs(grid, i, j));
            }
        }
    }
    return maxArea;
}

// DFS
private int dfs(int[][] grid, int a, int b) {

    // 该位置已超出矩阵限制或该位置值为0，结束搜索
    if (a < 0 || b < 0 || a >= grid.length || b >= grid[0].length || grid[a][b] == 0) { 
        return 0;
    } 

    // 将已搜索过的1赋值为0
    grid[a][b] = 0;


    // 记录1的个数
    int area = 1;

    // 递归搜索4个方向
    area += dfs(grid, a + 1, b);
    area += dfs(grid, a - 1, b);
    area += dfs(grid, a, b + 1);
    area += dfs(grid, a, b - 1);

    return area;
}