矩阵的遍历

对比

在深度优先和广度优先遍历时，我们经常需要从一个点向上下左右四个方向遍历，因此也就有了如下代码：

注意对比遍历的坐标：

public class TestString {
    public static int[][] dir = {{1, 0}, {-1, 0}, {0, -1}, {0, 1}};

    public static void main(String[] args) {
        TestString t = new TestString();
        t.test(0, 0);
    }

    public void test(int row, int col) {
        for (int[] d : dir) {
            row += d[0];
            col += d[1];
            System.out.print("row=" + row);
            System.out.println(", col=" + col);
        }

        System.out.println("+++++++++++++++++++++++++++");

        for (int[] d : dir) {
            System.out.print("row = ");
            System.out.print(row + d[0]);
            System.out.print(", col = ");
            System.out.println( col + d[1]);
        }
    }
}

结果如下：

row=1, col=0
row=0, col=0
row=0, col=-1
row=0, col=0
+++++++++++++++++++++++++++
row = 1, col = 0
row = -1, col = 0
row = 0, col = -1
row = 0, col = 1

 

对比可以发现，第二种才是我们需要的，第一种在遍历的时候更改了原始的坐标

 

深度优先遍历模板

class Solution {
    public static int[][] dir ={{1,0},{-1,0},{0,-1},{0,1}};
    private int m, n;
    private boolean[][] visited;

    public int numEnclaves(int[][] grid) {
        m = grid.length;
        n = grid[0].length;
        visited = new boolean[m][n];

        for (){
            ///
            dfs()
            ///
        }
    }


    public void dfs(int[][] grid, int row, int col){
        if (row<0 || row >=m || col <0 || col>=n || grid[row][col] == 0 || visited[row][col]){
            return;
        }
        visited[row][col] = true;
        for(int[] d: dir){
            dfs(grid, row+d[0], col+d[1]);
        }
    }
}