Odd-Even Subsequence (CF #651-D Binary Search)

#include <bits/stdc++.h>
using namespace std;
 
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

const int N = 2e5 + 5;

int n, k;
int a[N];

bool check(int x, int cur)
{
	int ans = 0;
	for(int i = 1; i <= n; i++)
	{
		if(!cur)
		{
			ans++;
			cur = 1;
		}
		else
		{
			if(a[i] <= x)
			{
				ans++;
				cur = 0;
			}
		}
	}
	return ans >= k;
}

int binsearch(int l, int h)
{
	while(l < h)
	{
		int m = (l + h) / 2;
		if(check(m, 0) || check(m, 1))
			h = m;
		else
			l = m + 1;
	}
	return l;
}

int main()
{
	IOS;
	cin >> n >> k;
	for(int i = 1; i <= n; i++)
		cin >> a[i];
	int ans = binsearch(1, 1e9);
	cout << ans;
	return 0;
}