Codeforces Round #439 B

The Eternal Immortality

题意：求a!/b! %10的值

思路：a-b>=5 答案即为0，小于5的直接模拟，中间可能爆long long，注意取模即可

AC代码：

#include "iostream"
#include "iomanip"
#include "string.h"
#include "stack"
#include "queue"
#include "string"
#include "vector"
#include "set"
#include "map"
#include "algorithm"
#include "stdio.h"
#include "math.h"
#pragma comment(linker, "/STACK:102400000,102400000")
#define bug(x) cout<<x<<" "<<"UUUUU"<<endl;
#define mem(a,x) memset(a,x,sizeof(a))
#define step(x) fixed<< setprecision(x)<<
#define mp(x,y) make_pair(x,y)
#define pb(x) push_back(x)
#define ll long long
#define endl ("
")
#define ft first
#define sd second
#define lrt (rt<<1)
#define rrt (rt<<1|1)
using namespace std;
const ll mod=998244353;
const ll INF = 1e18+1LL;
const int inf = 1e9+1e8;
const double PI=acos(-1.0);
const int N=1e5+100;

int main(){
    ll a,b,ans=1;
    cin>>a>>b;
    for(ll i=a+1; i<=b; ++i){
        ans*=i;
        ans%=10;
        if(ans==0){
            cout<<"0";
            return 0;
        }
    }
    cout<<ans;
    return 0;
}