牛客训练赛25-找规律+变相前缀和+差分

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<map>
#define ll long long
using namespace std;
const int mod = 1e9+7;
const int maxx=100005;
int n,m;
ll a[maxx];
ll s;
ll c[maxx];
ll ans[maxx];
int main(){
    int x,t;
   while(~scanf("%d%d",&n,&m)){
      memset(c,0,sizeof(c));
      memset(a,0,sizeof(a));
      s=0;
      for (int i=1;i<=n;i++){
        scanf("%lld",&a[i]);
        s=(a[i]+s)%mod;
        c[i]=(a[i]-a[1]+mod)%mod;
      }
      ll pre=s;
      ans[0]=a[1];
      for (int i=1;i<=100001;i++){
          ans[i]=(pre-a[1]+2*mod)%mod;
          a[1]=ans[i];
          pre=pre*(n-1)%mod;
      }
      while(m--){
        scanf("%d%d",&x,&t);
        ll anss;
        if (t%2==0) anss=(ans[t]+c[x])%mod;
        else anss=(ans[t]-c[x]+mod)%mod;
        printf("%lld\n",anss);
      }

   }
  return 0;
}