HDU – 6231 K-th Number(尺取+二分)

• 具体如下
• 用num计算当前区间中大于x的数的个数
• if(num<k)
  • 那么移动右端点，并判断a[++r]>=x
    • 是则++num
• else
  • 先判断num==k
    • 是则加上n-r+1
  • 再移动左端点，并判断a[l++]>=x
    • 是则–num
• 重复上述操作，直至r>n

#include<algorithm>
#include <iostream>
#include  <fstream>
#include  <cstdlib>
#include  <cstring>
#include  <cassert>
#include   <cstdio>
#include   <vector>
#include   <string>
#include    <cmath>
#include    <queue>
#include    <stack>
#include      <set>
#include      <map>
using namespace std;
#define P(a,b,c) make_pair(a,make_pair(b,c))
#define rep(i,a,n) for (int i=a;i<=n;i++)
#define per(i,a,n) for (int i=n;i>=a;i--)
#define CLR(vis) memset(vis,0,sizeof(vis))
#define MST(vis,pos) memset(vis,pos,sizeof(vis))
#define pb push_back
//#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef pair<int,pair<int,int> >pii;
typedef long long ll;
typedef unsigned long long ull;
const ll mod = 1000000007;
const ll INF = 1e18;
ll gcd(ll a, ll b) {
	return b ? gcd(b, a%b) : a;
}
template<class T>inline void gmax(T &A, T B) {
	(A<B)&&(A=B);//if(B>A)A=B;
}
template<class T>inline void gmin(T &A, T B) {
	(A>B)&&(A=B);//if(B<A)A=B;
}
template <class T>
inline bool scan(T &ret) {
	char c;
	int sgn;
	if(c=getchar(),c==EOF) return 0; //EOF
	while(c!='-'&&(c<'0'||c>'9')) c=getchar();
	sgn=(c=='-')?-1:1;
	ret=(c=='-')?0:(c-'0');
	while(c=getchar(),c>='0'&&c<='9') ret=ret*10+(c-'0');
	ret*=sgn;
	return 1;
}
inline void outt(int x) {
	if(x>9) outt(x/10);
	putchar(x%10+'0');
}

const int maxn = 1e5+10;
int a[maxn];
int b[maxn];

ll n,k,m;
bool check(int x){
	int l = 1;
	int r = 0;
	int num = 0;
	ll cnt = 0;
	while(r<=n){
		if(num<k){
			if(a[++r] >= x)num++;
		}else{
			if(num==k) cnt += n-r+1;
			if(a[l++] >= x)num--;
		}
	}
	if(cnt<m)return false;
	return true;
}

int main(){
	int t;
	scanf("%d", &t);
	while(t--){
		cin>>n>>k>>m;
		rep(i,1,n){
			scanf("%d", &a[i]);
			b[i] = a[i];
		}
		sort(b+1,b+n+1);
		int l = 1, r = n;
		while(l<r){
			int mid = (l+r+1)/2;
			if(check(b[mid])){
				l = mid;
			}else{
				r = mid-1;
			}
		}
		cout<<b[l]<<endl;
	}
	return 0;
}