输出字母沙漏

#include <bits/stdc++.h>
using namespace std;
int main() {
    int n;
    cin >> n;
    /* 以n=2为例 ABCBA共需要2*n+1=5个字节 */
    string s(2 * n + 1, ' ');
    /* 左右对称地进行赋值 */
    for (int i = 0; i <= n; ++i) s[i] = s[2 * n - i] = (char) ('A' + i);
    for (int i = 0; i <= n; ++i) {
        /* 第i行输出i个空格符 i的范围是从第0行到第n行 */
        for (int j = 0; j < i; ++j) cout << " ";
        /* 字母则从s串的第i个字符开始输出 直到第2*n-i个字符(对称位置) */
        for (int j = i; j <= 2 * n - i; ++j) cout << s[j];
        cout << endl;
    }
    for (int i = n - 1; i >= 0; --i) {
        for (int j = 0; j < i; ++j) cout << " ";
        for (int j = i; j <= 2 * n - i; ++j) cout << s[j];
        cout << endl;
    }
    return 0;
}