POJ 2014.K-th Number 区间第k大 （归并树）

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<map>
#include<queue>
#include<stack>
#include<vector>
#include<set>
using namespace std;
#define PI acos(-1.0)
typedef long long ll;
typedef pair<int,int> P;
const int maxn=5e5+100,maxm=1e5+100,inf=0x3f3f3f3f,mod=1e9+7;
const ll INF=1e13+7;
inline int get_int()
{
    int num=0;
    char ch;
    while((ch=getchar())!=‘ ‘&&ch!=‘\n‘)
        num=num*10+(ch-‘0‘);
    return num;
}
/****************************/
struct edge
{
    int from,to;
    int cost;
};
edge es[maxm];
struct node
{
    int num;
    int k;
};
node sign[maxn];
int a[maxn];
int cmp(node x,node y)
{
    return x.num<y.num;
}
vector<node>tree[maxn];
void build(int l,int r,int pos)
{
    if(l==r) return;
    int mid=(l+r)/2;
    for(int i=0; i<tree[pos].size(); i++)
    {
        int k=tree[pos][i].k;
        if(l<=k&&k<=mid) tree[pos<<1].push_back(tree[pos][i]);
        else tree[pos<<1|1].push_back(tree[pos][i]);
    }
    build(l,mid,pos<<1);
    build(mid+1,r,pos<<1|1);
}
int query(int L,int R,int w,int l,int r,int pos)
{
    ///cout<<l<<" "<<r<<endl;
    if(L<=l&&r<=R)
    {
        int s=0,e=tree[pos].size()-1;
        int cou=-1;
        while(s<=e)
        {
            int md=(s+e)/2;
            if(tree[pos][md].num<=w) s=md+1,cou=md;
            else e=md-1;
        }
        ///cout<<cou+1<<endl;
        return cou+1;
    }
    int mid=(l+r)/2;
    int ans=0;
    if(L<=mid) ans+=query(L,R,w,l,mid,pos<<1);
    if(R>mid) ans+=query(L,R,w,mid+1,r,pos<<1|1);
    return ans;
}
int main()
{
    int n,q;
    scanf("%d%d",&n,&q);
    for(int i=0; i<n; i++)
    {
        scanf("%d",&a[i]);
        sign[i].num=a[i],sign[i].k=i+1;
    }
    sort(sign,sign+n,cmp);
    for(int i=0; i<n; i++) tree[1].push_back(sign[i]);
    build(1,n,1);
    while(q--)
    {
        int l,r,k;
        scanf("%d%d%d",&l,&r,&k);
        int L=0,R=n-1;
        int ans=-1;
        while(L<=R)
        {
            int mid=(L+R)/2;
            int w=sign[mid].num;
            ///cout<<"x="<<w<<endl;
            if((query(l,r,w,1,n,1))>=k) R=mid-1,ans=mid;
            else L=mid+1;
        }
        cout<<sign[ans].num<<endl;
    }
    return 0;
}