【HDOJ6656】Kejin Player（期望DP）

题意：玩一个共有n级的游戏，i级出发每次可以花a[i]的代价，有p[i]的几率变成i+1级，有1-p[i]的几率变成x[i]级，x[i]<=i

多次询问，每次询问从l级升到r级的期望总代价

n,q<=5e5，0<=a[i]<=1e9

思路：

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef pair<ll,ll> Pll;
typedef vector<int> VI;
typedef vector<PII> VII;
#define N  1100000
#define M  4100000
#define fi first
#define se second
#define MP make_pair
#define pi acos(-1)
#define mem(a,b) memset(a,b,sizeof(a))
#define rep(i,a,b) for(int i=(int)a;i<=(int)b;i++)
#define per(i,a,b) for(int i=(int)a;i>=(int)b;i--)
#define lowbit(x) x&(-x)
#define Rand (rand()*(1<<16)+rand())
#define id(x) ((x)<=B?(x):m-n/(x)+1)
#define ls p<<1
#define rs p<<1|1

const ll MOD=1e9+7,inv2=(MOD+1)/2;
      double eps=1e-6;
      int INF=1e9;

ll s[N];

ll read()
{
   ll v=0,f=1;
   char c=getchar();
   while(c<48||57<c) {if(c=='-') f=-1; c=getchar();}
   while(48<=c&&c<=57) v=(v<<3)+v+v+c-48,c=getchar();
   return v*f;
}

ll pw(ll x,ll y)
{
    ll t=1;
    while(y)
    {
        if(y&1) t=t*x%MOD;
        x=x*x%MOD;
        y>>=1;
    }
    return t;
}

int main()
{
    //freopen("1.in","r",stdin);
    int cas;
    scanf("%d",&cas);
    while(cas--)
    {
        int n,q;
        scanf("%d%d",&n,&q);
        rep(i,0,n) s[i]=0;
        rep(i,1,n)
        {
            ll ri=read(),si=read(),xi=read(),ai=read();
            ll fi=(si*ai%MOD+(si-ri+MOD)*(s[i-1]-s[xi-1]+MOD)%MOD)%MOD*pw(ri,MOD-2)%MOD;
            //printf("i=%d fi=%I64d
",i,fi);
            s[i]=(s[i-1]+fi)%MOD;
        }
        rep(i,1,q)
        {
            int l,r;
            scanf("%d%d",&l,&r);
            //printf("l=%d r=%d
",l,r);
            printf("%I64d
",(s[r-1]-s[l-1]+MOD)%MOD);
        }
    }

    return 0;
}