[leetcode] 43. Multiply Strings(大数相乘)

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Multiply Strings

描述

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2.
Note:
1. The length of both num1 and num2 is < 110.
2. Both num1 and num2contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

我的代码

大数相乘：看代码中注意点

class Solution {
public:string multiply(string num1, string num2) {int len1 = num1.length();int len2 = num2.length();if (len1 == 0 || len2 == 0)  return "0";int *rlt = new int[(len1 + len2)];  //乘积的位数为len1+len2或者len1+len2-1memset(rlt, 0, (len1 + len2)*sizeof(int));for (int i = 0; i < len1; i++){for (int j = 0; j < len2; j++){rlt[i + j + 1] += (num1[i] - '0')*(num2[j] - '0');//之所以加个1是为了把首位空出来放进位}}for (int i = len1+len2-1; i >=1; i--){if (rlt[i] >= 10) //进位{rlt[i - 1] += (rlt[i] / 10);rlt[i] = rlt[i] % 10;}}int ind = 0;while ((rlt[ind] == 0) && ind < len1+len2-1) ind++; //去掉开头的0，要考虑结果为0的情况，不能输出如“0000”而要输出“0”string sRlt="";for (; ind < len1 + len2; ind++){sRlt += (rlt[ind] + '0');}delete[] rlt;return sRlt;}
};

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