HDU 6311 Harvest of Apples (组合数)

场上怎么都想不出来，看了标程想自闭。。。

#include <algorithm>
#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
using namespace std;
#define N 100005
#define mod 1000000007
struct query{
    int n,k,i;
}Q[N];
bool cmp(const query&a,const query&b){
    return a.n<b.n;
}
int reflect[N];///分块
vector<query>lis[2000];
int fac[N],inv[N];
int quick(int a,int b){
    int odd = 1;
    while (b){
        if(b&1)odd = 1ll*odd*a%mod;
        a = 1ll*a*a%mod;
        b>>=1;
    }
    return odd;
}
const int mx = 100000;
void deal(){
    fac[0] = 1;
    for(int i = 1 ; i <= mx ; ++i){
        fac[i] = 1ll*i*fac[i-1]%mod;
    }
    inv[mx] = quick(fac[mx],mod-2);
    for(int i = mx ; i ; --i){
        inv[i-1] = 1ll*i*inv[i]%mod;
    }
}
int res[N];
int C(int n,int m){
    return 1ll*fac[n]*inv[m]%mod*inv[n-m]%mod;
}
int main() {
    deal();
    int cent = sqrt(mx);
    int cnt = 1;
    for (int i = 1; i <= mx; i += cent, ++cnt) {
        for (int j = i; j <= mx and j <= i + cent; ++j) {
            reflect[j] = cnt;
        }
    }
    int T;
    scanf("%d",&T);
    for(int i = 1 ; i <= T ; ++i){
        scanf("%d %d",&Q[i].n,&Q[i].k);
        Q[i].i = i;
        lis[reflect[Q[i].k]].push_back(Q[i]);
    }
    for(int i = 1 ; i <= cnt ; ++i)if(!lis[i].empty()){
        sort(lis[i].begin(),lis[i].end(),cmp);
        int val = 0,in = lis[i][0].n,ik = -1;
        for(auto &j : lis[i]){
            while (in<j.n)val = (0ll + val + val + mod - C(in++,ik))%mod;
            while (ik<j.k)val = (val + C(in,++ik))%mod;
            while (ik>j.k)val = (val + mod - C(in,ik--))%mod;
            res[j.i] = val;
        }
    }
    for(int i = 1 ; i <= T ; ++i){
        printf("%d\n",res[i]);
    }
}

标程太秀了，顶礼膜拜。