leetcode（43）Multiply Strings

#include<iostream>
#include<vector>
#include<cstring>

using namespace std;

class Solution {
public:
    string multiply(string num1, string num2) {
        int n1 = num1.size(), n2 = num2.size();
        if (n1 == 0 || n2 == 0)
            return "";//空的话返回空
        if (num1[0] == '0' || num2[0] == '0')
            return "0";//如果有0的话返回"0"
        string res;
        vector<int> tmp(n1 + n2, 0);//tmp长度为m+n，初始化为0
        int k = n1 + n2 - 2;
        for (int i = 0; i<n1; i++)
        {
            for (int j = 0; j<n2; j++)
            {
                tmp[k - i - j] += (num1[i] - '0')*(num2[j] - '0');//这里顺序不要弄错，数字高位在前，保存到tmp向量末尾
            }
        }
        int c = 0;
        for (int i = 0; i<n1 + n2; i++)//处理进位
        {
            tmp[i] += c;
            c = tmp[i] / 10;
            tmp[i] %= 10;
        }
        int i = k + 1;
        //从不是0的最高位算起（因为结果可能小于m+n位）
        while (tmp[i] == 0)
            i--;
        for (; i >= 0; i--)
            res.push_back(tmp[i] + '0');
        return res;
    }
};

void main(void)
{
    string a = "1", b = "1";
    Solution p;
    string res;
    res = p.multiply(a, b);
    cout << res.c_str();
    system("pause");
}