算法题：杨辉三角打印

#include <iostream>
#include <vector>
using namespace std;
string Add(string s1,string s2)
{
    string my_str1(s1.rbegin(),s1.rend());
    string my_str2(s2.rbegin(),s2.rend());
    int len1 = my_str1.size();
    int len2 = my_str2.size();
    int flags = 0;
    string s;
    int i = 0;
    int j = 0;
    while (flags != 0 || i < len1 || j < len2)
    {
        char ch1 = my_str1[i];
        char ch2 = my_str2[j];
        if (i >= len1)
        {
            ch1 = '0';
        }
        if (j >= len2)
        {
            ch2 = '0';
        }
        if (ch1 - '0' + ch2 - '0' + flags-10>=0)
        {
            s += (ch1-'0' + ch2 - '0'-10+flags+'0');
            flags = 1;
        }
        else
        {
            s += flags + ch1 + ch2 - '0';
            flags = 0;
        }
        i++;
        j++;
    }
    return string(s.rbegin(),s.rend());
}
int main()
{
    int n;
    while (cin >> n&&n!=0)
    {
        vector<string> vtr((n+1)*n/2);
        int k = 0;
        for (int i = 0; i < n; i++)
        {
            vtr[k] = "1";
            vtr[k + i] = "1";
            int m = i-2;
            int j = k + 1;
            while (m>=0)
            {
                m--;
                //arr[j] = arr[j / 2 - 1]+arr[j/2];好吧，以前就犯过这个错误，这不是完全二叉树。
                vtr[j] = Add(vtr[j - i - 1],vtr[j - i]);
                j++;
            }
            k = k + i + 1;
        }
        k = 0;
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j <= i; j++)
            {
                cout << vtr[k++].c_str() << " ";
            }
            cout << endl;
            cout << endl;
        }
    }
    return 0;
}