算法竞赛入门经典（第2版）习题2-3

输入正整数，输出一个n层的倒三角形。

int main(){    unsigned n;    cin >> n;    int j = 2 * n - 1;    if (n <= 20)    {        for (int i = n; i >0; i--)        {            if (j==(2*n-1))            {                for (j=(2*n)-1; j > 0;j--)                    cout << "#";            }            else            {                for (int x = 0; x < (n - i); x++)                    cout << " ";                for (int y = 0; y <(2*i)-1; y++)                    cout << "#";                for (int q = 0; q < (n - i); q++)                    cout << " ";            }            j -= 2;            cout << endl;        }    }    return 0;}