这题用Java无敌

import java.math.BigInteger;
import java.util.Scanner;

public class Main
{
public static void main(String[] args)
{
Scanner scan=new Scanner(System.in);
BigInteger a=scan.nextBigInteger();
BigInteger b=scan.nextBigInteger();
BigInteger c=a.multiply(b);
System.out.println(c);
}

}

//没有压位。。。蜜汁过了lol
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

const int MAXN = 10005;
string s1, s2;

struct BigInt{
    int num[MAXN * 4], size;
    BigInt(string str){
        size = (int)str.size();
        for (int i = 0; i < str.size(); i++){num[i] = str[size - i - 1] - '0';}
    }
    BigInt operator*(BigInt b2){
        const int *num2 = b2.num;
        BigInt neu("");
        neu.size = b2.size + size;
        for (int i = 0; i < this -> size; i++){
            for (int j = 0; j < b2.size; j++){
                neu.num[i + j] += num2[j] * num[i];
            }
        }
        for (int i = 1; i < neu.size + 10; i++){
            neu.num[i] += neu.num[i - 1] / 10;
            neu.num[i - 1] %= 10;
        }
        for (int i = neu.size + 10; i >= 0; i--){
            if (neu.num[i] != 0) {neu.size = i + 1; break;}
        }
        return neu;
    }
    void print(){
        for (int i = this -> size - 1; i >= 0; i--){
            printf("%d", this -> num[i]);
        }
        printf("\n");
    }
};

int main(){
    cin >> s1 >> s2;
    BigInt b1(s1), b2(s2);
    BigInt neu = b1 * b2;
    neu.print();
    return 0;
}

print(int(input()) * int(input()))

人生苦短(

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
string tp;

struct u{
int A[10000],len;

//构造函数 指的是 一开始变量生成的时候做的初始化操作
u(){
memset(A,0,sizeof(A));
len=1;
}

u (string a){
memset(A,0,sizeof(A));
this->len=0;
for(int i=a.length()-1;i>=0;i--){
this->A[this->len]=a[i]-'0';
this->len++;
}
}
void pt(){
for(int i=this->len-1;i>=0;i--){
printf("%d",A[i]);
}
//printf("\n%d",len);
}

u operator * (u s)//重载运算符 *
{

u ans;
int maxlen=this->len+s.len+1;
for(int i=0;i<s.len;i++){
for(int j=0;j<this->len;j++){
ans.A[i+j]+=this->A[j]*s.A[i];
ans.A[i+j+1]+=ans.A[i+j]/10;
ans.A[i+j]%=10;
}
}
while(ans.A[maxlen]==0 && maxlen>0) maxlen--;
ans.len=maxlen+1;
return ans;
}

};

int main(){
cin>>tp;
u a(tp);
cin>>tp;
u b(tp);
u c=a*b;
c.pt();
return 0;
}

FFT

#include<iostream>
#include<cmath>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<cstring>
using namespace std;
const long double pi=acos(-1);
struct cp{long double x,y;};
cp operator +(cp a,cp b){return (cp){a.x+b.x,a.y+b.y};}
cp operator -(cp a,cp b){return (cp){a.x-b.x,a.y-b.y};}
cp operator *(cp a,cp b){return (cp){a.x*b.x-a.y*b.y,a.x*b.y+a.y*b.x};}
cp cur[1000005],a[1000005],b[1000005];
char ch[1000005];
int len1,len2,len,ans[1000005];
void fft(cp *a,int n,int fl){
for(int i=(n>>1),j=1;j<n;++j){
if(i<j)swap(a[i],a[j]);
int k;
for(k=(n>>1);k&i;i^=k,k>>=1);i^=k;
}
for(int m=2;m<=n;m<<=1){
cp w=(cp){cos(2*pi*fl/m),sin(2*pi*fl/m)};
cur[0]=(cp){1,0};
for(int j=1;j<(m>>1);j++)cur[j]=cur[j-1]*w;
for(int i=0;i<n;i+=m)
for(int j=i;j<i+(m>>1);++j){
cp u=a[j],v=a[j+(m>>1)]*cur[j-i];
a[j]=u+v;
a[j+(m>>1)]=u-v;
}
}
if(fl==-1)
for(int i=0;i<n;i++)
a[i]=(cp){a[i].x/n,a[i].y/n};
}
int main(){
scanf("%s",ch);
len1=strlen(ch);
for(int i=len1-1;i>=0;i--)a[len1-i-1]=(cp){ch[i]-'0',0};
scanf("%s",ch);
len2=strlen(ch);
for(int i=len2-1;i>=0;i--)b[len2-i-1]=(cp){ch[i]-'0',0};
len=1;
while(len<(len1+len1)||len<(len2+len2))len<<=1;
for(int i=len1;i<len;i++)a[i]=(cp){0,0};
for(int i=len2;i<len;i++)b[i]=(cp){0,0};
fft(a,len,1);fft(b,len,1);
for(int i=0;i<len;i++)a[i]=a[i]*b[i];
fft(a,len,-1);
for(int i=0;i<len;i++)ans[i]=a[i].x+0.5;
for(int i=0;i<len;i++)ans[i+1]+=ans[i]/10,ans[i]%=10;
while(!ans[len-1]&&len)len--;
for(int i=len-1;i>=0;i--)printf("%d",ans[i]);
printf("\n");
return 0;
}

QAQ

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<queue>
#include<cstdlib>
#include<cmath>
#define maxn 100005
using namespace std;
char s1[maxn],s2[maxn];
int c[maxn],a1[maxn],a2[maxn];
void mul(int a[],int b[]){
    for(int i=1;i<=a[0];i++){
        for(int j=i;j<=b[0]+i-1;j++){
            c[j]+=a[i]*b[j-i+1];
            if(c[j]>=10){
                c[j+1]+=c[j]/10;
                c[j]=c[j]%10;
            }
        }
    }c[0]=a[0]+b[0];
    while(c[c[0]]==0&&c[0]>0){c[0]--; }
    while(c[c[0]+1]){
        c[0]++;
        c[c[0]+1]+=c[c[0]]/10;
        c[c[0]]%=10;
    }
} 
int main(){
    scanf("%s%s",s1+1,s2+1);
    int len1=strlen(s1+1),len2=strlen(s2+1);
    for(int i=1;i<=len1;i++){
        a1[i]=s1[len1-i+1]-'0';
    }
    for(int i=1;i<=len2;i++){
        a2[i]=s2[len2-i+1]-'0';
    }a1[0]=len1,a2[0]=len2;
    mul(a1,a2);
    for(int i=c[0];i>=1;i--){
        printf("%d",c[i]);
    }
}

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <queue>
#include <stack>
using namespace std;

int main()
{
char a[10000] , b[10000];
int n[10000]={} , m[10000]={} , result[10000] = {};
int la , lb , i , j , w = 0;
int k = w;
cin >> a >> b;
la = strlen(a);
lb = strlen(b);
for(i = 0;i < la;i++) n[i] = a[la-i-1] - '0';
for(i = 0;i < lb;i++) m[i] = b[lb-i-1] - '0';
for(i = 0;i < la;i++)
for(j = 0;j < lb;j++)
{
result[i + j] += n[i] * m[j];
if(result[i + j] != 0) w = i + j;
}
for(i = 0;i <= w + 5;i++)
{
result[i + 1] += result[i] / 10;
result[i] %= 10;
if(result[i] != 0) k = i;
}
for(i = k;i >= 0;i--) cout << result[i];
return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <queue>
#include <stack>
using namespace std;

int main()
{
char a[10000] , b[10000];
int n[10000]={} , m[10000]={} , result[10000] = {};
int la , lb , i , j , w = 0;
int k = w;
cin >> a >> b;
la = strlen(a);
lb = strlen(b);
for(i = 0;i < la;i++) n[i] = a[la-i-1] - '0';
for(i = 0;i < lb;i++) m[i] = b[lb-i-1] - '0';
for(i = 0;i < la;i++)
for(j = 0;j < lb;j++)
{
result[i + j] += n[i] * m[j];
if(result[i + j] != 0) w = i + j;
}
for(i = 0;i <= w + 5;i++)
{
result[i + 1] += result[i] / 10;
result[i] %= 10;
if(result[i] != 0) k = i;
}
for(i = k;i >= 0;i--) cout << result[i];
return 0;
}

好短的主函数
#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
char cd[100000];
void maint(char ak[10001],char bk[10001])
{
int a[100000],b[100000],c[100001],d,e,f,z=0;
memset(a,0,sizeof(a));
memset(b,0,sizeof(b));
memset(c,0,sizeof(c));
d=strlen(ak);
e=strlen(bk);
for(int i=0;i<=d-1;++i)
{
a[d-i]=ak[i]-48;
}
for(int j=0;j<=e-1;++j)
{
b[e-j]=bk[j]-48;
}
for(int q=1;q<=d;++q)
{
z=0;
for(int v=1;v<=e;++v)
{
c[q+v-1]=a[q]*b[v]+z+c[q+v-1];
z=c[q+v-1]/10;
c[q+v-1]=c[q+v-1]%10;
}
c[q+e]=z;
}
f=d+e;
while((c[f]==0)&&(f>1))
{
f--;
}
for(int u=1;u<=f;++u)
{
cd[u]=0;
}
for(int u=f;u>=1;u--)
{
cd[f-u]=c[u]+48;
}
cout<<cd;
}
int main()
{
char a[10001],b[10001];
cin>>a>>b;
maint(a,b);
}

#include "stdio.h"
#include "string.h"

struct BigInt{
    int len;
    int nums[100000];
};

int main(){
    struct BigInt a, b, c;
    memset(&a, 0, sizeof(a));
    memset(&b, 0, sizeof(b));
    memset(&c, 0, sizeof(c));
    
    char input[100000];
    scanf("%s", input);
    for(int i = strlen(input) - 1; i >= 0 ; i--){
        a.nums[a.len++] = input[i] - 48;
    }
    
    scanf("%s", input);
    for(int i = strlen(input) - 1; i >= 0 ; i--){
        b.nums[b.len++] = input[i] - 48;
    }
    
    c.len = a.len + b.len;
    
    for(int i = 0; i < a.len; i++){
        for(int j = 0; j < b.len; j++){
            c.nums[i+j] = c.nums[i+j] + a.nums[i] * b.nums[j];
        }
    }
    
    for(int i = 0; i < c.len; i++){
        c.nums[i+1] = c.nums[i] / 10 + c.nums[i+1];
        c.nums[i] = c.nums[i] % 10;
    }
    
    while (c.nums[c.len] == 0 && c.len > 0){
        c.len--;
    }
    
    for(int i = c.len; i >= 0; i--){
        printf("%d", c.nums[i]);
    }
    
    printf("\n");
    
    return 0;
}
 

--Haskell一行

main = print . product . map read . words =<< getContents

#include <cstdio>
#include <string>
#include <algorithm>
#include <iostream>
using namespace std;
#define MAX 1
// D[i] : 0....99999
int pow_int(int a,int n)
{
    int count=1,x=a;
    while(n>0)
    {
        if(n&1)
            count*=x;
        x=x*x;
        n=n>>1;
    }
    return count;
}
struct BigInt
{
    int D[100000];       
    int max;
    int n;
    BigInt(int x)
    {
        fill(D,D+100,0);
        int i;
        max=pow_int(10,MAX);
        for(i=0;x>0;i++)
        {
            D[i]=x%max;
            x=x/max;
        }
        n=i;
    }
    BigInt(void)    
    {
        fill(D,D+100,0);
        n=0;
        max=pow_int(10,MAX);
    }
    void print(void)
    {
        cout<<D[n-1];   
        for(int i=n-2;i>=0;i--)
        {
            cout<<D[i]; 
        }
        cout<<endl;
    }
};
BigInt &mul(BigInt &a,BigInt &b);
int main()
{
    string s1,s2;
    cin>>s1>>s2;
    BigInt a,b;
    for(int i=s1.size()-1,j=0;i>=0;i--,j++)
        a.D[j]=s1[i]-'0';
    a.n=s1.size();
    for(int i=s2.size()-1,j=0;i>=0;i--,j++)
        b.D[j]=s2[i]-'0';
    b.n=s2.size();
    BigInt result=mul(a,b);
    result.print();
    return 0;
}

BigInt &mul(BigInt &a,BigInt &b)
{
    BigInt *result=new BigInt(0);
    for(int i=0;i<a.n;i++)
    {
        for(int j=0;j<b.n;j++)
        {
            result->D[i+j]+=a.D[i]*b.D[j];
            if(result->D[i+j]>=result->max)
                result->D[i+j+1]+=result->D[i+j]/result->max;
                result->D[i+j]=result->D[i+j]%result->max;
        }
    }
    result->n=a.n+b.n-1;
    
    while(result->D[result->n]==0&&result->n>1)
    {
        result->n--;
    }
    if(result->D[result->n])
        result->n++;
    return *result;
}

#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <cctype>
#include <vector>
#include <queue>
#include <set>
#include <bitset>
#include <cassert>
#include <map>
#include <string>
#include <sstream>
#include <ctime>
using namespace std;
int a[20010],b[20010],c[20010];
char s1[20010],s2[20010],s3[20010];
int main()
{
int la,lb,l;
scanf("%s%s",s1,s2);
la=strlen(s1);
lb=strlen(s2);
for(int i=1;i<=la;i++)
{
a[i]=s1[la-i]-'0';
}
for(int i=1;i<=lb;i++)
{
b[i]=s2[lb-i]-'0';
}
for(int i=1;i<=la;i++)
{
for(int j=1;j<=lb;j++)
{
c[i+j-1]=c[i+j-1]+a[i]*b[j];
c[i+j]=c[i+j]+c[i+j-1]/10;
c[i+j-1]=c[i+j-1]%10;
}
}
l=la+lb;
while(c[l]==0&&l>1)
{
l--;
}
for(int i=l;i>=1;i--)
{
printf("%d",c[i]);
}
return 0;
}

裸题~

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <iomanip>
#include <cstdlib>
using namespace std;

char str1[10002],str2[10002];
int a[10002],b[10002],c[20010];
int c1,c2;

void init()
{
    for(int i=0;i<c1;i++)
        a[c1-i-1]=str1[i]-'0';
    for(int i=0;i<c2;i++)
        b[c2-i-1]=str2[i]-'0';
}

int main()
{
    scanf("%s %s",str1,str2);
    c1=strlen(str1);
    c2=strlen(str2);
    init();
    for(int i=0;i<c1;i++)
        for(int j=0;j<c2;j++)
        {
            c[i+j]+=a[i]*b[j];
            if(c[i+j]>=10)
                c[i+j+1]+=c[i+j]/10,c[i+j]%=10;
        }
    int k;
    for(k=c1+c2;k>=0;k--)
        if(c[k]!=0) break;
    for(int i=k;i>=0;i--)
        cout<<c[i];
    return 0;
}
     

注意前面的0

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<algorithm>

using namespace std;

int main()
{
string s1,s2;
cin>>s1>>s2;
int a[10001];
int b[10001];
int ans[100005];
memset(a,0,sizeof(a));
memset(b,0,sizeof(b));
memset(ans,0,sizeof(ans));
a[0]=s1.length();
b[0]=s2.length();
for(int i=1;i<=a[0];i++)
{
a[i]=s1[a[0]-i]-'0';
}
for(int i=1;i<=b[0];i++)
{
b[i]=s2[b[0]-i]-'0';
}
int w,x=0;
w=a[0]+b[0];
for(int i=1;i<=a[0];i++)
{
x=0;
for(int j=1;j<=b[0];j++)
{
ans[i+j-1]=a[i]*b[j]+x+ans[i+j-1];
x=ans[i+j-1]/10;
ans[i+j-1]=ans[i+j-1]%10;
}
ans[i+b[0]]=x;
}
while(ans[w]==0&&w>1)
w--;
for(int i=w;i>=1;i--)
{
cout<<ans[i];
}
return 0;
}

#include <stdio.h>
#include <string.h>
char anss[110000000];
char * multipy(char * a, char * b)
{
int i,j,la,lb,l,k;
la=strlen(a);
lb=strlen(b);
l=la+lb;
char ans[l+1];
memset(ans,0,sizeof(ans));
//for(i=0;i<l;i++)printf("%d",ans[i]);
for (i=la-1;i>=0;i--)
{
//printf("i=%d\n",i);
for(j=lb-1;j>=0;j--)
{
//printf("j=%d\n",j);
k=l-la-lb+i+j+1;//printf("pre_ans[%d]=%d\n",k,ans[k]);
ans[k]+=(a[i]-'0')*(b[j]-'0');
ans[k-1]+=ans[k]/10;
ans[k]=ans[k]%10;
//printf("ans[%d]=%d\n",k,ans[k]);
}
}
k=0;
while(ans[k]!=0) k--;
if(ans[0]==0)i=1; else i=0;
for (j=i;j<l;j++) anss[j-i]=ans[j]+'0';//printf("%d",ans[i]);
return anss;
}
int main()
{
char input1[10001],input2[10001];
scanf("%s %s",input1,input2);
printf("%s",multipy(input1,input2));
return 0;
}

调了半天 才发现result开的10000+位
幡然醒悟应该开20000位
#include <cstdio>
#include <cstring>
#define Q 6000
#define clear(a) memset(a,0,Q*sizeof(int))

void input(int a[]){
clear(a);
char c[11000];
scanf("%s",c);
int len=1,k=1;
for(int i=strlen(c)-1;i>=0;i--){
if(k==10000)
k=1,len++;
a[len]+=k*(c[i]-'0');
k*=10;
}
a[0]=len;
}

void mult(int a[],int b[],int c[]){
clear(c);
for(int i=1;i<=a[0];i++)
for(int j=1;j<=b[0];j++){
c[i+j-1]+=a[i]*b[j];
c[i+j]+=c[i+j-1]/10000;
c[i+j-1]%=10000;
}
int len=a[0]+b[0];
while(len>1&&c[len]==0)len--;
c[0]=len;
}

void output(int a[]){
printf("%d",a[a[0]]);
for(int i=a[0]-1;i>=1;i--)
printf("%04d",a[i]);
}

int main(){
freopen("in.txt","r",stdin);
int x[Q],y[Q],r[Q];
input(x);
input(y);
mult(x,y,r);
output(r);
return 0;
}

蒟蒻写的非常简单的代码，并没有用FFT或者压位什么的
但是居然AC了......
供参考
c++
#include <cstdio>
#include <cstring>
using namespace std;
int a[10001],b[10001],c[20001];
char s1[10001],s2[10001];
int main() {
gets(s1);gets(s2);
int i,j,l1=strlen(s1),l2=strlen(s2),x=0;
for (i=1;i<=l1;i++) a[i]=s1[l1-i]-48;
for (i=1;i<=l2;i++) b[i]=s2[l2-i]-48;
for (i=1;i<=l1;i++)
for (j=1;j<=l2;j++)
c[i+j]+=a[i]*b[j];
for (i=1;i<=l1+l2;i++) { //统一整理进位
c[i+1]+=c[i]/10;
c[i]%=10;
}
int max=l1+l2+1;
while (c[max]==0) max--; //去除数字前的零
for (i=max;i>=2;i--) printf("%d",c[i]);
printf("\n");
return 0;
}


#include<bits/stdc++.h>
using namespace std;
char A[50000000],B[5000000];
long long a[5000000],b[5000000],c[5000000];

int main()
{
int i,j,k=0,n,m,x;
long long l;
cin>>A>>B;
n=strlen(A); m=strlen(B);
strrev(A); strrev(B);

memset(a,0,sizeof(a)) ; memset(b,0,sizeof(b)) ; memset(c,0,sizeof(c)) ;
for(i=0;i<n;i++) a[i]=A[i]-48; for(i=0;i<m;i++) b[i]=B[i]-48;
k=0;
for (i=0;i<n;i++)
for (j=0;j<m+1;j++)
{
c[i+j] = c[i+j] + a[i] * b[j] +k;
k= c[i+j] / 10 ;
c[i+j] = c[i+j] % 10 ;
}
k=22000;
while (c[k]==0) k--;
for(i=k;i>=0;i--) cout<<c[i];
cout<<endl;
return 0;
}

某语言一行
print int(raw_input())*int(raw_input())