32分求助，感谢大佬！！！

aciel @ 2023-03-07 14:07:26

#include <iostream>
#include <queue>
using namespace std;
int n;
int a[31][31];
int v[31][31];//1表示标记
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};

struct node
{
    int x;
    int y;
}st,tx;
queue <node> q;

int bfs(int x,int y)
{
    st.x=x;
    st.y=y;
    v[x][y]=1;
    q.push(st);

    while(!q.empty())
    {
        st=q.front();
        q.pop();

        for(int i=0;i<4;i++){//四个方向
            tx.x=st.x+dx[i];
            tx.y=st.y+dy[i];
            //此处是0 并且未访问过  未出界
            if(a[tx.x][tx.y]==0&&v[tx.x][tx.y]==0&&tx.x>=0&&tx.x<=n+1&&tx.y>=0&&tx.y<=n+1){
                v[tx.x][tx.y]=1;
                q.push(tx);
            }
        }
    }

}

int main()
{

    cin>>n;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin>>a[i][j];
        }
    }
    bfs(0,0);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            if(v[i][j]==0&&a[i][j]==0){
                a[i][j]=2;
            }
            cout<<a[i][j]<<" ";
        }
        cout<<endl;
    }
    return 0;
}

by Smithespics @ 2023-03-12 09:42:48

顺便附上本蒟蒻的代码，整体思想跟你一直都是BFS，我这里的起点选取比较特殊。

#include<iostream>
#include<queue>
using namespace std;
int arr[40][40];
int dx[4] = {1,0,-1,0};
int dy[4] = {0,1,0,-1};

int main()
{
    queue<pair<int,int>> q;
    int n;
    int xx,yy;
    cin >> n;
    for(int i = 1;i <= n;i++)
        for(int j = 1;j <= n;j++)
            cin >> arr[i][j];

    int flag = 0;
    for(int i = 1;i <= n;i++)
    {
        for(int j = 1;j <= n;j++)
        {
            if(arr[i-1][j] && arr[i-1][j-1] && arr[i][j-1] && !arr[i][j])
            {
                xx = i;
                yy = j;
                q.push(make_pair(xx,yy));
                arr[xx][yy] = 2;
                flag = 1;
                break;
            }
        }
        if(flag == 1)
            break;
    }

    while(!q.empty())
    {
        xx = q.front().first;
        yy = q.front().second;
        q.pop();
        int sx,sy;
        for(int i = 0;i < 4;i++)
        {
            sx = xx + dx[i];
            sy = yy + dy[i];
            if(!arr[sx][sy] && sx <= n && sx >= 1 && sy <= n && sy >= 1)
            {
                arr[sx][sy] = 2;
                q.push(make_pair(sx,sy));
            }
        }
    }

    for(int i = 1;i <= n;i++)
    {
        for(int j = 1;j <= n;j++)
            cout << arr[i][j] << ' ';
        cout << endl;
    }
    return 0;
}

by Smithespics @ 2023-03-12 09:44:10

@aciel

我本蒟蒻觉得你这里的BFS函数中的判断条件有问题，如果这种情况输入的话就会导致外圈全部判定为2，输出结果错误，其次起点的选取的话要从0,0把全部的点而且程序整体的时间复杂度很高。

输入：

20

0 0 0 0 1 1 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 1 1 1 1 1 0 1 1 1 1 1 1 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 0 1 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 1 1 1 0 0 0 0