LC695

//需要自己指定开始位置（循环寻找）

int dx[4]={1,-1,0,0};
    int dy[4]={0,0,1,-1};
    int vis[55][55];

    int bfs(vector<vector<int>>& grid,int x,int y){
        int res=1;
        queue<pair<int,int> > q;
        q.push({x,y});
        vis[x][y]=1;
        int n=grid.size();
        int m=grid[0].size();
        while(!q.empty()){
            int x1=q.front().first;
            int y1=q.front().second;
            q.pop(); 
            for(int i=0;i<4;i++){
                int nx=x1+dx[i];
                int ny=y1+dy[i];
                if(nx>=0&&ny>=0&&nx<n&&ny<m&&grid[nx][ny]&&!vis[nx][ny]){
                    res++;
                    vis[nx][ny]=1;
                    q.push({nx,ny});
                }
            }
        }
       // cout<<res<<endl;
        return res;
    
    }

    int maxAreaOfIsland(vector<vector<int>>& grid) {
        int ans=0;
        memset(vis,0,sizeof(1));
        int n=grid.size();
        int m=grid[0].size();
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j]&&!vis[i][j]){
                    int res=bfs(grid,i,j);
                    ans=max(ans,res);
                }
            }   
        }
        return ans;
    }