题目描述

输入两个整数n和m，输出一个n行m列的矩阵，将数字 1 到 n*m 按照回字蛇形填充至矩阵中。

具体矩阵形式可参考样例。

输入格式

输入共一行，包含两个整数n和m。

输出格式

输出满足要求的矩阵。

矩阵占n行，每行包含m个空格隔开的整数。

数据范围

$1≤n,m≤100$

样例

3 3

1 2 3
8 9 4
7 6 5

写法1

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

int main() {
    int n, m; cin >> n >> m;
    vector<vector<int> > v(n, vector<int>(m, 0));
    int left = 0, right = m - 1, up = 0, down = n - 1, cur = 1;
    while (true) {
        for (int i = left; i <= right; i ++ ) v[up][i] = cur ++ ;
        up ++ ;
        if (up > down) break;
        for (int i = up; i <= down; i ++ ) v[i][right] = cur ++ ;
        right -- ;
        if (left > right) break;
        for (int i = right; i >= left; i -- ) v[down][i] = cur ++ ;
        down -- ;
        if (up > down) break;
        for (int i = down; i >= up; i --) v[i][left] = cur ++ ;
        left ++ ;
        if (left > right) break;
    }

    for (int i = 0; i < n; i ++ ) {
        for (int j = 0; j < m; j ++ )
            cout << v[i][j] << ' ';
        cout << endl;
    }

    return 0;
}

写法2

#include <iostream>
using namespace std;

const int N = 110;

int ret[N][N], n, m;
// 这里的方向一定要按照 右->下->左->上 的顺序写
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};

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

    for (int i = 0, j = 0, k = 1, d = 0; k <= n * m; k ++ ) {
        ret[i][j] = k;
        int a = i + dx[d], b = j + dy[d];
        // 出界或者该位置已经有值了
        if (a < 0 || b < 0 || a >= n || b >= m || ret[a][b]) {
            d = (d + 1) % 4;
            a = i + dx[d], b = j + dy[d];
        }
        i = a, j = b;
    }

    for (int i = 0; i < n; i ++ ) {
        for (int j = 0; j < m; j ++ )
            cout << ret[i][j] << ' ';
        cout << endl;
    }

    return 0;
}