题目来源：101. 孤岛的总面积

C++题解：在卡码网KamaCoder 100. 岛屿的最大面积-CSDN基础上加了个孤岛flg进行修改

#include <iostream>
#include <vector>
#include <queue>

#include <stdio.h>
using namespace std;
 
int res = 0, tmp = 0;
bool flg = false;
 
int bfs(vector<vector<int>> &grid, vector<vector<int>>&visited, int &tmp, int x, int y, bool& flg){
    queue<pair<int, int>> que;
    que.push({x, y});
    
    if(visited[x][y]==1 || grid[x][y] == 0) return tmp;
    if(x == 1 || x == grid.size()-1 || y == 1 || y == grid[0].size()-1) flg = true;
    visited[x][y] = true;
    tmp = tmp + 1;
    
    if(x-1 > 0) {
        if(grid[x-1][y] == 1 && visited[x-1][y] == 0){
            que.push({x-1, y});
        }
    }
    if(y-1 > 0) {
        if(grid[x][y-1] == 1 && visited[x][y-1] == 0){
            que.push({x, y-1});
        }
    }
    if(x+1 < grid.size()) {
        if(grid[x+1][y] == 1 && visited[x+1][y] == 0){
            que.push({x+1, y});
        }
    }
    if(y+1 < grid[0].size()) {
        if(grid[x][y+1] == 1 && visited[x][y+1] == 0){
            que.push({x, y+1});
        }
    }
    
    while(!que.empty()){
        pair<int, int> cur = que.front();
        que.pop();
        int curx = cur.first, cury = cur.second;
        tmp = bfs(grid, visited, tmp, curx, cury, flg);
    }
    
    return tmp;
    
}
 
int main(){
    int N, M;
    cin >> N >> M;
    vector<vector<int>> grid(N+1, vector<int>(M+1, 0));
    for(int i = 1; i <= N; i++) {
        for(int j = 1; j <= M; j++) {
            cin>>grid[i][j]; 
        }
    }
    
    vector<vector<int>> visited(N+1, vector<int>(M+1, 0));
    for(int i = 1; i <= N; i++) {
        for(int j = 1; j <= M; j++) {
            if(visited[i][j] == 1) continue;
            tmp = 0;
            flg = false;
            tmp = bfs(grid, visited, tmp, i, j, flg);
            if(!flg) res = res + tmp;
        }
    }
    
    cout<<res;
    return 0;
}