https://leetcode.com/problems/multiply-strings/description/

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Example 1:

Input: num1 = "2", num2 = "3"
Output: "6"

Example 2:

Input: num1 = "123", num2 = "456"
Output: "56088"

Note:

  1. The length of both num1 and num2 is < 110.
  2. Both num1 and num2 contain only digits 0-9.
  3. Both num1 and num2 do not contain any leading zero, except the number 0 itself.
  4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

我就不懂为啥自己这么一个大一就应该会的题能卡一个上午，还要看题解？？？？

好好反省吧QAQ

class Solution {
public:
    string multiply(string num1, string num2) {
        string num(num1.size()+num2.size(),'0');
        for(int i=num1.size()-1;i>=0;i--){
            for(int j=num2.size()-1;j>=0;j--){
                int pro=(num1[i]-'0')*(num2[j]-'0')+num[i+j+1]-'0';
                num[i+j+1]=pro%10+'0';
                num[i+j]=pro/10+num[i+j];
            }
        }
        int e=num.find_first_not_of("0");
        return e<0?"0":num.substr(e);
    }
};