[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.

 

 大数的乘法问题，运用乘法规则就好了。

class Solution {
public:
    string multiply(string num1, string num2) {
        if(num1=="0" || num2=="0") return "0";
        string result;
        int len1=num1.length();
        int len2=num2.length();
        int len=len1+len2;
        int* n1=new int[len1];
        int* n2=new int[len2];
        int* multi=new int[len];
        for(int i=0;i<len;i++)
        {
            multi[i]=0;
        }
        for(int i=0;i<len1;i++)
        {
            n1[i]=num1[len1-i-1]-'0';
        }
        for(int i=0;i<len2;i++)
        {
            n2[i]=num2[len2-i-1]-'0';
        }
        for(int i=0;i<len1;i++)
        {
            for(int j=0;j<len2;j++)
            {
                multi[i+j]=multi[i+j]+n1[i]*n2[j];
            }
        }
        for (int i=0;i<len;i++)
        {
            int tmp=multi[i];
            multi[i]=tmp%10;
            multi[i+1]+=tmp/10;
        }
        int first_nozero;
        for(int i=len-1;i>=0;i--)
        {
            if(multi[i]!=0)
            {
                first_nozero=i;
                break;
            }
        }
        for(int i=first_nozero;i>=0;i--)
        {
            result+=char(multi[i]+'0');
        }
        delete []n1;
        delete []n2;
        delete []multi;
        
        return result;
    }
};