#include<iostream>
using namespace std;
long long n,s=0,n1,i;
int main()
{
    cin>>n>>n1;
    i=n;
    
        while(i<=n1)
        {
            if(i+40000000000000<=n1)
            i+=40000000000000,s+=9700000000000;
            else
                if(i+40000000000<=n1)
                i+=40000000000,s+=9700000000;
                else
                    if(i+4000000<=n1)
                    i+=4000000,s+=970000;
                    else
                    for(i;i<=n1;i++)
                    if(i%400==0||i%4==0&&i%100!=0) s++;
        }
    
    cout<<s;
    return 0;
}
//可以化简一下

绝对不超时

#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int main()
{
    long long a,b,i,s=0;
    cin>>a>>b;
    i=a;
    for(;i<=b;)
    {
        if((i%4==0&&i%100!=0)||(i%400==0&&i+400>b))
        {
            s++;
        }
        while(i+40000000000000<=b)
        {
            i+=40000000000000;
            s+=9700000000000;
        }
        while(i+40000000000<=b)
        {
            i+=40000000000;
            s+=9700000000;
            if(i%40000000000000==0&&i+40000000000000<=b) break;
        }
        while(i%40000000==0&&i+40000000<=b)
        {
            i+=40000000;
            s+=9700000;
            if(i%40000000000==0&&i+40000000000<=b) break;
        }
        while(i%400000==0&&i+400000<=b)
        {
            i+=400000;
            s+=97000;
            if(i%40000000==0&&i+40000000<=b) break;
        }
        while(i%400==0&&i+400<=b)
        {
            i+=400;
            s+=97;
            if(i%400000==0&&i+400000<=b) break;
        }
        i++;
    }
    if(a%400==0||a%4==0&&a%100!=0) s++;
    if(b%400==0||b%4==0&&b%100!=0) s++;
    cout<<s;
    //fixed<<setprecision()
    return 0;
}

不超时的代码

#include<iostream>
using namespace std;
int main()
{
long long a,b,m=0;
cin>>a>>b;
for(long long i=a;i<=b;i++)
{
if(i==0)
m+=0;
else
{
if((i%100==0&&i%400==0)||(i%100!=0&&i%4==0))
m++;
}

}
cout<<m;
return 0;
}