leetcode——1254.统计封闭岛屿的数目

像这种DFS相关的题型，重点还是要知道如何进行标记。我就是卡在这里顺不下去，难过死了……

public int closedIsland(int[][] grid) {
        int sum = 0;
        for(int i = 1;i<grid.length;i++){
            for(int j = 1;j<grid[0].length;j++){
                if(grid[i][j] == 0){
                    if(findIsland(grid,i,j)){
                        sum++;
                    }
                }
            }
        }
        return sum;
    }

    private boolean findIsland(int[][] grid, int i, int j) {
        if(i<0||i>=grid.length||j<0||j>=grid[0].length){
            return false;
        }
        if(grid[i][j] == 1){
            return true;
        }
        grid[i][j] = 1;
        boolean up = findIsland(grid,i-1,j);
        boolean down = findIsland(grid,i+1,j);
        boolean left = findIsland(grid,i,j-1);
        boolean right = findIsland(grid,i,j+1);

        return up && down && left && right;
    }

 

 用debug的方式很容易理解一道题解的思路。

——2020.6.21