参考答案：

#include<iostream>

using namespace std;

int main()
{
    char a = 'A', b, c;

    cin >> c;
    for (int i = a; i <= c; ++i)
    {
        for (int j = i; j < c; ++j) cout << ' ';
        for (int j = a; j <= i; ++j) printf("%c", j);
        for (int j = i - 1; j >= a; --j) printf("%c", j);
        cout << endl;
    }

    return 0;
}