模拟法 出界或已经遍历过就改变方向

#include<bits/stdc++.h>
using namespace std;
const int N = 110;
int g[N][N];
int n, m;
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};

void bfs(){
    int x = 1, y = 1; g[1][1] = 1;
    int t = 0;
    for(int i = 2; i <= n * m; ++ i){
        int a = x + dx[t], b = y + dy[t];
        if(a < 1 || a > n || b < 1 || b > m || g[a][b]) {
            t = (t + 1) % 4; a = x + dx[t], b = y + dy[t];
        }
        g[a][b] = i;
        x = a, y = b;
    }
}

int main(){
    cin >> n >> m;
    bfs();
    for(int i = 1; i <= n; ++ i){
        for(int j = 1; j <= m; ++ j){
            cout << g[i][j] << ' ';
        }
        cout << '\n';
    }
    return 0;
}