POJ2104

主席树板子

找区间第k小的数+离散化

// Problem: K-th Number
// Contest: POJ - Northeastern Europe 2004
// URL: http://poj.org/problem?id=2104
// Memory Limit: 65 MB
// Time Limit: 20000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
typedef long long ll;
const int N=1e5+9;
struct node{
	int l,r;
	ll c;
}seg[N<<5];
#define tl(id) seg[id].l
#define tr(id) seg[id].r
int a[N];
vector<int> X;
int root[N],index;
int binary(int x){
	return lower_bound(X.begin(),X.end(),x)-X.begin()+1;
}
void pushup(int id){
	seg[id].c=seg[tl(id)].c+seg[tr(id)].c;
}
void insert(int post,int &curr,int l,int r,int v){
	curr=++index;
	seg[curr]=seg[post];
	if(l==r){
		seg[curr].c++;
		return;
	}
	int mid=(l+r)>>1;
	if(mid>=v){
		insert(tl(post),tl(curr),l,mid,v);
	}else{
		insert(tr(post),tr(curr),mid+1,r,v);
	}
	pushup(curr);
}
ll query(int post,int curr,int l,int r,int k){
	ll c=seg[tl(curr)].c-seg[tl(post)].c;
	if(l==r){
		return l;
	}
	int mid=(l+r)>>1;
	if(c>=k){
		return query(tl(post),tl(curr),l,mid,k);
	}else{
		return query(tr(post),tr(curr),mid+1,r,k-c);
	}
}
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	int n,m;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	for(int i=1;i<=n;i++){
		X.push_back(a[i]);
	}
	sort(X.begin(),X.end());
	X.erase(unique(X.begin(),X.end()),X.end());
	int XN=X.size();
	for(int i=1;i<=n;i++){
		insert(root[i-1],root[i],1,XN,binary(a[i]));
	}
	for(int i=1;i<=m;i++){
		int l,r,k;
		cin>>l>>r>>k;
		cout<<X[query(root[l-1],root[r],1,XN,k)-1]<<'\n';
	}
	return 0;
}