multiply-strings

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.

程序：

class Solution {public:    string multiply(string num1, string num2) {        int carry = 0;        string result(num1.size()+num2.size(),'0');        for (int i=num1.size()-1;i>=0;--i) {            int a = num1[i] - '0';            for (int j=num2.size()-1;j>=0;--j) {                int b = num2[j] - '0';                int c = result[i+j+1] - '0';                int v = a*b+c+carry;                result[i+j+1] = v%10 + '0';                carry = v/10;            }            if(carry){                result[i] = carry+'0';                carry = 0;            }        }        int i = 0;        while (i<result.size()&&result[i]=='0') ++i;        return i==result.size()?"0":result.substr(i);    }};

点评：

大数乘法