【leetcode】Multiply Strings

Multiply Strings

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.

 

 

各个位相乘，保存在数组中，最后再处理进位。

如

123*456

 

  4,5,6

     8,10,12

        12,15,18

________________

   4,13,28,27,18

 

即56088

 

class Solution {
public:
    string multiply(string num1, string num2) {
       
        if(num1=="0"||num2=="0") return "0";
       
        while(num1[0]=='0') num1.erase(0);
        while(num2[0]=='0') num2.erase(0);
       
        int n1=num1.size();
        int n2=num2.size();
       
        int *numArr1=new int[n1];
        int *numArr2=new int[n2];
       
        int *result=new int[n1+n2];
        memset(result,0,sizeof(int)*(n1+n2));
        for(int i=0;i<n1;i++) numArr1[i]=num1[i]-'0';
        for(int i=0;i<n2;i++) numArr2[i]=num2[i]-'0';
       
        for(int i=0;i<n1;i++)
        {
            for(int j=0;j<n2;j++)
            {
                result[i+j+1]+=numArr1[i]*numArr2[j];
            }
        }
       
        int carry=0;
        for(int i=n1+n2-1;i>=0;i--)
        {
            result[i]+=carry;
            if(result[i]>=10)
            {
                carry=result[i]/10;
                result[i]=result[i]%10;
            }
            else
            {
                carry=0;
            }
        }
       
        string resultStr;
        int k=0;
        while(result[k]==0) k++;
       
        for(int i=k;i<n1+n2;i++)
        {
            resultStr.push_back(result[i]+'0');
        }
       
        return resultStr;
    }
};