[LeetCode]Multiply Strings

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.

思考：大数相乘，模拟算数运算。

class Solution {
public:
    string multiply(string num1, string num2) {
        if(num1=="0"||num2=="0") return "0";
        int len1=num1.size();
        int len2=num2.size();
        int len=len1+len2;
        string num3(len,'0');
        int i,j;
        for(j=len2-1;j>=0;j--)
        {
            for(i=len1-1;i>=0;i--)
            {
				int temp=(num2[j]-'0')*(num1[i]-'0')+(num3[i+j+1]-'0');
                if(temp>9) num3[i+j+1]=temp%10+'0';
				else num3[i+j+1]=temp+'0';
				num3[i+j]=((num3[i+j]-'0')+temp/10)+'0';
            }
        }
        if(num3[0]!='0') return num3;
        else return num3.substr(1,len-1);
    }
};