代码

#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const int N=1e5+9;

string add(string s1,string s2) {
	string s;
	int len1=s1.length();
	int len2=s2.length();
	if(len1>len2) {
		for(int i=1;i<=len1-len2;++i) s2='0'+s2;
	}
	else {
		for(int i=1;i<=len2-len1;++i) s1='0'+s1;
	}
	int a=s1.length();
    int temp,cf=0;
    for(int i=a-1;i>=0;--i) {
    	temp=s1[i]-'0'+s2[i]-'0'+cf;
    	cf=temp/10;
    	temp%=10;
    	s=char(temp+'0')+s;
    }
    if(cf) s=char(cf+'0')+s;
    return s;
}

string sub(string s1,string s2) {
	string s;
	int len1=s1.length();
	int len2=s2.length();
	if(len1>len2) {
		for(int i=1;i<=len1-len2;++i) s2='0'+s2;
	}
	else {
		for(int i=1;i<=len2-len1;++i) s1='0'+s1;
	}
	if(s1<s2) {
		string ss=sub(s2,s1);
		s.erase(0,s.find_first_not_of('0'));
		ss='-'+ss;
		return ss;
	}
	int a=s1.length();
	int temp,cf=0;
	for(int i=a-1;i>=0;--i) {
		temp=s1[i]-'0'-(s2[i]-'0')+cf;
		if(temp<0) {
			cf=-1;
			temp+=10;
		}
		else cf=0;
		s=char(temp+'0')+s;
	}
	s.erase(0,s.find_first_not_of('0'));
	return s;
}

string mul(string str1,string str2)
{
    string str;
    int len1=str1.length();
    int len2=str2.length();
    string tempstr;
    for(int i=len2-1;i>=0;i--)
    {
        tempstr="";
        int temp=str2[i]-'0';
        int t=0;
        int cf=0;
        if(temp!=0)
        {
            for(int j=1;j<=len2-1-i;j++)
              tempstr+="0";
            for(int j=len1-1;j>=0;j--)
            {
                t=(temp*(str1[j]-'0')+cf)%10;
                cf=(temp*(str1[j]-'0')+cf)/10;
                tempstr=char(t+'0')+tempstr;
            }
            if(cf!=0) tempstr=char(cf+'0')+tempstr;
        }
        str=add(str,tempstr);
    }
    str.erase(0,str.find_first_not_of('0'));
    return str;
}

void solve() {
	string s1,s2;cin>>s1>>s2;
	string s=mul(s1,s2);
	cout<<s;
} 


int main() {
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	int _;_=1;
	while(_--) solve();
	return 0;
}

评测结果