Codeforces Round #390 (Div. 2), problem: (D) Fedor and Coupons Solution in C/C++

Codeforces Round #390 (Div. 2), problem: (D) Fedor and Coupons Solution in C/C++

#include <bits/stdc++.h>
#include <iostream>
#include <queue>
#include <set>
using namespace std;
#define mp make_pair
#define fi first
#define se second
typedef long long ll;
ll n,k,ans,l;
priority_queue<ll>s;
struct item
{
	ll x,y,pos;
}a[333333];
bool cmp(item a, item b)
{
	return a.x<b.x;
}
int main()
{
	cin>>n>>k;
	for(ll i=1;i<=n;i++)
	{
		scanf("%lld%lld",&a[i].x,&a[i].y);
		a[i].pos=i;
	}
	sort(a+1,a+n+1,&cmp);
	for(ll i=1;i<=n;i++)
	{
		if(s.size()<k)
			s.push(-a[i].y);
		else if(-s.top()<a[i].y)
			s.pop(),s.push(-a[i].y);
		if(ans<-s.top()-a[i].x+1&&s.size()==k)
			ans=-s.top()-a[i].x+1,
			l=a[i].x;
	}
	cout<<ans<<endl;
	if(ans==0)
	{
		for(ll i=1;i<=k;i++)
			printf("%lld ",i);
		return 0;
	}
	for(ll i=1;i<=n&&k;i++)
		if(a[i].x<=l&&l+ans-1<=a[i].y)
			printf("%lld ",a[i].pos),k--;
}