HIHOCODER 1420 Bigint Multiplication

Posted 2020-10-15

描述

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Given 2 nonnegative integers a and b, calculate a × b.

输入

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One line with 2 integers a and b separated by a single space.
0 ≤ a, b ≤ 10100.

输出

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The value of a × b.

样例输入

100000000000000000000 100000000000000000000

样例输出

10000000000000000000000000000000000000000

注意很多0时只要输出一个

#include <bits/stdc++.h>
#define ll long long
#define inf 1000000000
#define PI acos(-1)
#define bug puts("here")
#define REP(i,x,n) for(int i=x;i<=n;i++)
#define DEP(i,n,x) for(int i=n;i>=x;i--)
#define mem(a,x) memset(a,x,sizeof(a))
using namespace std;
inline int read(){
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
const int N=205;
class BigNumber{
    public:
    char a[N];
    int tot;
    BigNumber(char t[]){
         tot=0;
         DEP(i,strlen(t)-1,0) a[tot++]=t[i];
    }
    BigNumber(){tot=0;}
};
BigNumber Add (BigNumber an,BigNumber bn){
     int mn=max(bn.tot,an.tot),sum,add=0;
     BigNumber tmp;
     REP(i,0,mn-1){
         sum=0;
         if(i<bn.tot) sum+=bn.a[i]-'0';
         if(i<an.tot) sum+=an.a[i]-'0';
         sum+=add;
         add=sum/10;sum%=10;
         tmp.a[i]=sum+'0';
     }
     tmp.tot=mn;
     if(add!=0) tmp.a[tmp.tot++]=add+'0';
     return tmp;
}
BigNumber s1 (int s,BigNumber bn){
      int sum,add=0;
      BigNumber tmp;
      REP(i,0,bn.tot-1){
          sum=s*(bn.a[i]-'0')+add;
          add=sum/10;sum%=10;
          tmp.a[i]=sum+'0';
      }
      tmp.tot=bn.tot;
      if(add!=0) tmp.a[tmp.tot++]=add+'0';
      return tmp;
}
BigNumber multi (BigNumber an,BigNumber bn){
      BigNumber c1,t;
      int sum,add;
      REP(i,0,an.tot-1){
          t=s1(an.a[i]-'0',bn);
          if(i!=an.tot-1){
             DEP(j,bn.tot-1,0) bn.a[j+1]=bn.a[j];
             bn.a[0]='0';
             bn.tot++;
          }
          c1=Add(c1,t);
      }
      return c1;
}
char t1[N],t2[N];
int main(){
   // while(1)
    {
        cin>>t1>>t2;
        BigNumber ans=multi(BigNumber(t1),BigNumber(t2));
        bool flag=false;
        REP(i,0,ans.tot-1) if(ans.a[i]!='0') {flag=true;break;}
        if(!flag) {puts("0");return 0;}
        DEP(i,ans.tot-1,0) printf("%c",ans.a[i]);
        puts("");
    }
    return 0;
}