Multiply Strings -- leetcode

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.

用字符串表示的整数，做乘法运算。

如人工做乘法运算的步骤一样，实现了本算法。

在leetcode上实际执行时间为12ms。

class Solution {
public:
    string multiply(string num1, string num2) {
        if (num1.empty() || num2.empty()) return "";

        vector<int> temp(num1.size()+num2.size());

        for (int i=num1.size()-1; i>=0; i--) {
                int k = temp.size()-num1.size()+i;
                int carry = 0;
                const int digit1 = num1[i] - '0';
                for (int j=num2.size()-1; j>=0; j--, k--) {
                        temp[k] += digit1 * (num2[j] - '0') + carry;
                        carry = temp[k] / 10;
                        temp[k] %= 10;
                }
                while (carry) {
                        temp[k] += carry;
                        carry = temp[k] / 10;
                        temp[k] %= 10;
                        k--;
                }
        }

        string result;
        for (int i=0; i<temp.size(); i++) {
                if (temp[i] || !result.empty())
                        result += temp[i] + '0';
        }

         return result.empty() ? "0" : result;
    }
};

Multiply Strings -- leetcode

原文：http://blog.csdn.net/elton_xiao/article/details/42843201