牛客57、61（图）

牛客57.岛屿数量

dfs

import java.util.*;


public class Solution {
    /**
     * 判断岛屿数量
     * @param grid char字符型二维数组 
     * @return int整型
     */
    public int solve (char[][] grid) {
        int n = grid.length;
        if (n == 0)
            return 0;
        int m = grid[0].length;
        int count = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (grid[i][j] == '1') {
                    count++;
                    dfs(grid, i, j);
                }
            }
        }
        return count;
    }
    public void dfs(char[][] grid, int i, int j) {
        int n = grid.length;
        int m = grid[0].length;
        grid[i][j] = '0';
        if (i - 1 >= 0 && grid[i - 1][j] == '1')
            dfs(grid, i - 1, j);
        if (i + 1 < n && grid[i + 1][j] == '1')
            dfs(grid, i + 1, j);
        if (j - 1 >= 0 && grid[i][j - 1] == '1')
            dfs(grid, i, j - 1);
        if (j + 1 < m && grid[i][j + 1] == '1')
            dfs(grid, i, j + 1);
    }
}

 

 

牛客61.矩阵最长递增路径

dfs

import java.util.*;


public class Solution {
    private int[][] dirs = new int[][] {{-1,0}, {1,0}, {0,-1},{0,1}};
    private int n, m;
    public int dfs (int[][] matrix, int[][] dp, int i, int j) {
        if (dp[i][j] != 0)
            return dp[i][j];
        dp[i][j]++;
        for (int k = 0; k < 4; k++) {
            int nexti = i + dirs[k][0];
            int nextj = j + dirs[k][1];
            if (nexti >= 0 && nexti < n && nextj >= 0 && nextj < m && matrix[nexti][nextj] > matrix[i][j])
                dp[i][j] = Math.max(dp[i][j], dfs(matrix, dp, nexti,nextj) + 1);
        }
        return dp[i][j];
    }
    public int solve (int[][] matrix) {
        if (matrix.length == 0 || matrix[0].length == 0)
            return 0;
        int res = 0;
        n = matrix.length;
        m = matrix[0].length;
        int[][] dp = new int[m + 1][n + 1];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                res = Math.max(res, dfs(matrix, dp, i, j));
            }
        }
        return res;
    }
    
}