【正经题解】回形取数

#include <bits/stdc++.h>
using namespace std;

int main(){
    int n, m;
    cin >> n >> m;

    int a[1001][1001], cnt = 0;
    // 初始化数字矩阵
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            a[i][j] = ++cnt;
        }
    }

    // 回形搜索
    int x = 1, y = 1;
    cout << a[x][y];
    a[x][y] = 0;
    for (int i = 2; i <= n * m; i++) {
        // 1往下
        while (x + 1 <= n and a[x + 1][y] != 0) {
            cout << "," << a[++x][y];
            a[x][y] = 0;
        }
        // 2往右
        while (y + 1 <= m and a[x][y + 1] != 0) {
            cout << "," << a[x][++y];
            a[x][y] = 0;
        }
        // 3往上
        while (x - 1 >= 1 and a[x - 1][y] != 0) {
            cout << "," << a[--x][y];
            a[x][y] = 0;
        }
        // 4往左
        while (y - 1 >= 1 and a[x][y - 1] != 0) {
            cout << "," << a[x][--y];
            a[x][y] = 0;
        }
    }

    return 0;
}