UVA 10106 Product （大數相乘）

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Product 

The Problem

The problem is to multiply two integers X, Y. (0<=X,Y<10250)

The Input

The input will consist of a set of pairs of lines. Each line in pair contains one multiplyer.

The Output

For each input pair of lines the output line should consist one integer the product.

Sample Input

12122222222222222222222222222

Sample Output

144444444444444444444444444

大數相乘，網上有很多模板，今下午練練手，自己寫一遍，剛開始忽略了前置0，導致0*12=00,0*123=000，後來改了輸出就ac了。

#include <iostream>#include <cstring>#define maxn 260using namespace std;int main(){    char str1[maxn],str2[maxn];    while(cin>>str1>>str2){int len1,len2;len1=strlen(str1);len2=strlen(str2);int s1[maxn],s2[maxn];memset(s1,0,sizeof(s1));memset(s2,0,sizeof(s2));int i;for(i=0;i<len1;i++)s1[i]=str1[i]-'0';for(i=0;i<len2;i++)s2[i]=str2[i]-'0';int sum[maxn+maxn];memset(sum,0,sizeof(sum));int j,k;for(i=len2-1;i>=0;i--){for(j=len1-1;j>=0;j--){sum[i+j+1]=sum[i+j+1]+s2[i]*s1[j];}}for(k=len1+len2-1;k>=0;k--)if(sum[k]>=10){int temp;temp=sum[k]%10;sum[k-1]=sum[k-1]+sum[k]/10;sum[k]=temp;}//if(sum[0]!=0)//cout<<sum[0];bool flag=0;for(i=0;i<len1+len2-1;i++){if(sum[i]!=0)flag=1;if(flag==1)cout<<sum[i];}cout<<sum[len1+len2-1];cout<<endl;}    return 0;}