200.岛屿数量(DFS M-岛屿系列)

    /**
     * @param {character[][]} grid
     * @param {number} r
     * @param {number} c
     * @param {number} rSize
     * @param {number} cSize
     * @return
     */
    function dfs(grid, r, c, rSize, cSize) {
        // 如果这个格子坐标超出或者不是岛屿，直接返回
        if (!(0 <= r && r < rSize && 0 <= c && c < cSize) || grid[r][c] !== '1') {
            return
        }
        //标记已经遍历过的点
        grid[r][c] = '2'
        // 访问上、下、左、右四个相邻结点
        dfs(grid, r - 1, c, rSize, cSize)
        dfs(grid, r + 1, c, rSize, cSize)
        dfs(grid, r, c - 1, rSize, cSize)
        dfs(grid, r, c + 1, rSize, cSize)
    }

    /**
     * @param {character[][]} grid
     * @return {number}
     */
    var numIslands = function (grid) {
        let rSize = grid.length
        let cSize = grid[0].length
        let res = 0
        for (let r = 0; r < rSize; ++r) {
            for (let c = 0; c < cSize; ++c) {
                if (grid[r][c] === '1') {
                    ++res
                    dfs(grid, r, c, rSize, cSize)
                }
            }
        }
        return res
    }