Leetcode 43. Multiply StringsI

题意

用数字字符串模拟乘法。

题解

如题

代码

class Solution {public:    string mulStr(int digit, string num)    {        string result;        int carry = 0;        for (int i = num.length() - 1; i >= 0; i--)        {            int temp = digit * (num[i] - '0') + carry;            carry = temp / 10;            result += (temp % 10 + '0');        }        if (carry != 0)            result += (carry + '0');        reverse(result.begin(), result.end());        return result;    }    string addStr(string num1, string num2)    {        if (num1.length() == 0)            return num2;        string result;        //int min_size = min(num1.length(), num2.length());        int carry = 0;        int i,j;        for (i = num1.length() - 1, j = num2.length() - 1;  i >= 0 && j >= 0; i--, j--)        {            int temp = num1[i] - '0' + num2[j] - '0' + carry;            carry = temp / 10;            result += (temp % 10 + '0');        }        while (i >= 0)        {            int temp = (num1[i] - '0' + carry);            carry = temp / 10;            result += (temp % 10 + '0');            i--;        }        while (j >= 0)        {            int temp = (num2[j] - '0' + carry);            carry = temp / 10;            result += (temp % 10 + '0');            j--;        }        if (carry != 0)            result += (carry + '0');        reverse(result.begin(), result.end());        return result;    }    string multiply(string num1, string num2) {        if (num1 == "0" || num2 == "0")            return "0";        string result;        if (num1.length() < num2.length())        {            swap(num1, num2);        }        for (int i = num2.length() - 1; i >= 0; i--)        {            string temp = mulStr(num2[i] - '0', num1);            string zeros(num2.length() - 1 - i, '0');            //temp += zeros;            result = addStr(result, temp + zeros);        }        return result;    }};