LeetCode OJ 之 Multiply Strings（字符串乘积）

题目：

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

给两个字符串代表两个数字，以字符串形式返回这两个数字的乘积。

注意：数字是任意大的，而且是非负的。

思路：

模拟乘数运算。

代码：

class Solution {
public:
    string multiply(string num1, string num2) 
    {
        int len1 = num1.size();
        int len2 = num2.size();
        string result;

        if(num1[0] == '0' || num2[0] == '0')
            return "0";
        int *num = new int[len1+len2]();
        for(int i = len1 - 1 ; i >= 0 ; i--)
        {
            for(int j = len2 - 1 ; j >= 0 ; j--)
            {
                num[i+j+1] += (num1[i] - '0') * (num2[j] - '0');
            }
        }
        for(int i = len1+len2-1 ; i >= 0 ; i--)
        {
            if(i > 0)
                num[i-1] += num[i]/10;
            num[i] %= 10;
            result = char(num[i]+'0') + result;
        }
        delete [] num;
        if(result[0] == '0')
            return result.substr(1);
        else
            return result;
    
    }
};