Educational Codeforces Round 52 (Rated for Div. 2) E. Side Transmutations

http://codeforces.com/contest/1065/problem/E

数学推导题

 #include <bits/stdc++.h>
 using namespace std;
 #define ll long long
 #define minv 1e-6
 #define inf 1e9
 #define pi 3.1415926536
 #define nl 2.7182818284
 const ll mod=;
 const int maxn=1e5+;

 ll mul(ll a,ll b)
 {
     ll y=;
     while (b)
     {
         if (b & )
             y=y*a%mod;
         b>>=;
         a=a*a%mod;
     }
     return y;
 }

 int main()
 {
     int n,m,g,b,preb,len,i;
     ll sum=,v;
     scanf("%d%d%d",&n,&m,&g);
     preb=;
     for (i=;i<=m;i++)
     {
         scanf("%d",&b);
         len=b-preb;
         v=mul(g,len);
         sum=(sum*v%mod*(v+)%mod*)%mod;
         preb=b;
     }
     v=mul(g,n-*b);
     sum=sum*v%mod;
     cout<<sum;
     return ;
 }