很奇怪，题目上明明说n是2到20，但是如果只给array开21，提交就会RE，22就可以AC。。。
#include<iostream>
#include<string>
#include <array>
#include<math.h>
#include<algorithm>
using namespace std;int main()
{int n; cin >> n;string s;cin >> s;int row = s.length();row = ceil(row / n);array<array<char, 22>, 22>charmat;for (int i = 0; i < row; i++) {for (int j = 0; j < n; j++) {charmat[i][j]=s[i*n+j];}if (i % 2) {reverse(charmat[i].begin(), charmat[i].begin() + n);}}for (int j = 0; j < n; j++) {for (int i = 0; i < row; i++) {cout << charmat[i][j];}}//for (int i = 0; i < row; i++) {// for (int j = 0; j < n; j++) {// cout << charmat[i][j] << " ";// }// cout << endl;//}return 0;
}