B. Jzzhu and Sequences1300 / 思维 规律

Posted 2021-12-08 幽殇默

https://codeforces.com/contest/450/problem/B
找规律，发现6个为一组是一个循环节。

#include<bits/stdc++.h>
using namespace std;
typedef long long int LL;
const int N=1e5+10;
const int mod=1e9+7;
LL f[N];
int main(void)
{
	LL x,y,n; cin>>x>>y>>n;
	f[1]=(x+mod)%mod,f[2]=(y+mod)%mod;
	for(int i=3;i<=6;i++) f[i]=(f[i-1]-f[i-2]+mod)%mod;
	int cnt=n%6;
	if(cnt==0) cnt=6;
	cout<<f[cnt]<<endl;
	return 0;
}