[LeetCode] Multiply Strings 解题报告

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.

» Solve this problem

[解题思路]
大整数乘法，一位一位往上乘，注意进位的处理即可。此外，注意0的处理

[Code]

1:    string multiply(string num1, string num2) {  2:      // Start typing your C/C++ solution below  3:      // DO NOT write int main() function  4:      if(num1.size() ==0 || num2.size() ==0) return 0;  5:      string res(num1.size()+num2.size()+1, '0');  6:      std::reverse(num1.begin(), num1.end());  7:      std::reverse(num2.begin(), num2.end());  8:      for(int i =0; i < num1.size(); i++)  9:      {  10:        int dig1 = num1[i] -'0';  11:        int carry = 0;  12:        for(int j = 0; j< num2.size(); j++)  13:        {  14:          int dig2 = num2[j] - '0';  15:          int exist = res[i+j] -'0';          16:          res[i+j] = (dig1*dig2+carry+ exist) % 10 +'0';    17:          carry = (dig1*dig2+carry+exist)/10;  18:        }  19:        if(carry >0)  20:        {  21:          res[i+num2.size()] = carry + '0';  22:        }  23:      }  24:      std::reverse(res.begin(), res.end());  25:      int start =0;  26:      while(res[start] =='0' && start < res.size())  27:      {  28:        start++;  29:      }  30:      if(start == res.size()) return "0";  31:      return res.substr(start, res.size()-start);  32:    }

[Note]
1. Line 25~31, 处理乘法过程中在起始处产生的0。比如， “9133”， “0”，直接乘的结果是“000000”，而期待结果是“0”

转载于:https://www.cnblogs.com/codingtmd/archive/2012/12/28/5078984.html

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