牛客网：NC109 岛屿数量

使用dfs

import java.util.*;


public class Solution {
    
    // 深度优先 dfs 把结果修改
    public int solve (char[][] grid) {
        // write code here
        int m = grid.length;
        if (m == 0){
            return 0;
        }
        int n = grid[0].length;
        int ans = 0;
        for (int i = 0; i < m ; i ++){
            for (int j = 0; j < n; j++){
                if (grid[i][j] == '1'){
                    ans++;
                    dfs(grid, i , j);
                }
            }
        }
        return ans;
    }
    
    private void dfs(char[][] grid, int i, int j){
        grid[i][j] = '0';
        int m = grid.length;
        int n = grid[0].length;
        if (i - 1 >= 0 && grid[i - 1][j] == '1'){
            dfs(grid, i - 1, j);
        }
        if (i + 1 < m && 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 < n && grid[i][j + 1] == '1'){
            dfs(grid, i , j + 1);
        }
        
    }
}

使用bfs

import java.util.*;


public class Solution {
    
    // 广度优先
    public int solve (char[][] grid) {
        // write code here
        int m = grid.length;
        if (m == 0){
            return 0;
        }
        int n = grid[0].length;
        int ans = 0;
        for (int i = 0; i < m; i++){
            for (int j = 0; j < n; j++){
                if (grid[i][j] == '1'){
                    grid[i][j] = '0';
                    ans++;
                    Queue row = new LinkedList<>();
                    Queue col = new LinkedList<>();
                    row.offer(i);
                    col.offer(j);
                    while (!row.isEmpty()){
                        int r = row.poll();
                        int c = col.poll();
                        if (r - 1 >= 0 && grid[ r - 1][c] == '1'){
                            row.offer(r - 1);
                            col.offer(c);
                            grid[r - 1][c] = '0';
                        }
                        
                        if (r + 1 < m && grid[r + 1][c] == '1'){
                            row.offer(r + 1);
                            col.offer(c);
                            grid[r + 1][c] = '0';
                        }
                        
                        if (c - 1 >= 0 && grid[r][c -  1] == '1'){
                            row.offer(r);
                            col.offer(c - 1);
                            grid[r][c - 1] = '0';
                        }
                        
                        if (c + 1 < n && grid[r][ c +  1] == '1'){
                            row.offer(r);
                            col.offer(c + 1);
                            grid[r][c + 1] = '0';
                        }
                    }
                 }
            }
           
        }
         return ans;
    }
}