卡码网KamaCoder 100. 岛屿的最大面积

题目来源：100. 岛屿的最大面积

C++题解：

1. 广度优先搜索。使用队列存储，一层一层地往外扩展。

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

int res = 0, tmp = 0;

int bfs(vector<vector<int>> &grid, vector<vector<int>>&visited, int &tmp, int x, int y){
    queue<pair<int, int>> que;
    que.push({x, y});
    
    if(visited[x][y]==1 || grid[x][y] == 0) return tmp; 
    
    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);
    }
    
    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;
            tmp = bfs(grid, visited, tmp, i, j);
            res = max(res, tmp);
        }
    }
    
    
    cout<<res;
    return 0;
}

2. 深度优先搜索。一个点走到尽头再去找下一个。

#include <iostream>
#include <vector>
using namespace std;
 
int res = 0, tmp = 0;
 
 
int dfs(vector<vector<int>> &grid, vector<vector<int>>&visited, int &tmp, int x, int y){
    if(visited[x][y]==1 || grid[x][y] == 0) return tmp; 
    visited[x][y] = true;
    tmp = tmp + 1;
    if(x-1 > 0) {
        if(grid[x-1][y] == 1 && visited[x-1][y] == 0){
            tmp = dfs(grid, visited, tmp, x-1, y);
        }
    }
    if(y-1 > 0) {
        if(grid[x][y-1] == 1 && visited[x][y-1] == 0){
            tmp = dfs(grid, visited, tmp, x, y-1);
        }
    }
    if(x+1 < grid.size()) {
        if(grid[x+1][y] == 1 && visited[x+1][y] == 0){
            tmp = dfs(grid, visited, tmp, x+1, y);
        }
    }
    if(y+1 < grid[0].size()) {
        if(grid[x][y+1] == 1 && visited[x][y+1] == 0){
            tmp = dfs(grid, visited, tmp, x, y+1);
        }
    }
    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;
            tmp = dfs(grid, visited, tmp, i, j);
            res = max(res, tmp);
        }
    }
     
     
    cout<<res;
    return 0;
}