luogu P1712 [NOI2016]区间 贪心 尺取法 线段树 二分

//#include<bits/stdc++.h>
#include<iostream>
#include<cstdio>
#include<ctime>
#include<cctype>
#include<queue>
#include<deque>
#include<stack>
#include<iostream>
#include<iomanip>
#include<cstdio>
#include<cstring>
#include<string>
#include<ctime>
#include<cmath>
#include<cctype>
#include<cstdlib>
#include<queue>
#include<deque>
#include<stack>
#include<vector>
#include<algorithm>
#include<utility>
#include<bitset>
#include<set>
#include<map>
#define ll long long
#define db double
#define INF 1000000001
#define ldb long double
#define pb push_back
#define put_(x) printf("%d ",x);
#define get(x) x=read()
#define gt(x) scanf("%d",&x)
#define gi(x) scanf("%lf",&x)
#define put(x) printf("%d\n",x)
#define putl(x) printf("%lld\n",x)
#define rep(p,n,i) for(RE int i=p;i<=n;++i)
#define go(x) for(int i=lin[x],tn=ver[i];i;tn=ver[i=nex[i]])
#define fep(n,p,i) for(RE int i=n;i>=p;--i)
#define vep(p,n,i) for(RE int i=p;i<n;++i)
#define pii pair<int,int>
#define mk make_pair
#define RE register
#define P 1000000007ll
#define gf(x) scanf("%lf",&x)
#define pf(x) ((x)*(x))
#define uint unsigned long long
#define ui unsigned
#define EPS 1e-4
#define sq sqrt
#define S second
#define F first
#define mod 998244353
#define l(p) t[p].l
#define r(p) t[p].r
#define sum(p) t[p].sum
#define zz p<<1
#define yy p<<1|1
using namespace std;
char *fs,*ft,buf[1<<15];
inline char gc()
{
	return (fs==ft&&(ft=(fs=buf)+fread(buf,1,1<<15,stdin),fs==ft))?0:*fs++;
}
inline int read()
{
	RE int x=0,f=1;RE char ch=gc();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=gc();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=gc();}
	return x*f;

}
const int MAXN=500010;
int n,m,cnt,num;
struct wy
{
	int l,r;
	int sum;
}t[MAXN<<3],s[MAXN];
inline int cmp(wy a,wy b){return a.sum<b.sum;}
int a[MAXN],b[MAXN],tag[MAXN<<3],c[MAXN<<1];
inline void build(int p,int l,int r)
{
	l(p)=l;r(p)=r;
	if(l==r)return;
	int mid=(l+r)>>1;
	build(zz,l,mid);
	build(yy,mid+1,r);
}
inline void pushdown(int p)
{
	tag[zz]+=tag[p];
	tag[yy]+=tag[p];
	sum(zz)+=tag[p];
	sum(yy)+=tag[p];
	tag[p]=0;
}
inline void change(int p,int l,int r,int x)
{
	if(l<=l(p)&&r>=r(p))return sum(p)+=x,tag[p]+=x,void();
	int mid=(l(p)+r(p))>>1;
	if(tag[p])pushdown(p);
	if(l<=mid)change(zz,l,r,x);
	if(r>mid)change(yy,l,r,x);
	sum(p)=max(sum(zz),sum(yy));
}
int main()
{
	//freopen("1.in","r",stdin);
	get(n);get(m);
	rep(1,n,i)
	{
		get(s[i].l);get(s[i].r);
		c[++num]=s[i].l;
		c[++num]=s[i].r;
	}
	sort(c+1,c+1+num);
	rep(1,num,i)if(i==1||c[i]!=c[i-1])c[++cnt]=c[i];
	rep(1,n,i)
	{
		s[i].sum=s[i].r-s[i].l;
		s[i].r=lower_bound(c+1,c+1+cnt,s[i].r)-c;
		s[i].l=lower_bound(c+1,c+1+cnt,s[i].l)-c;
	}
	sort(s+1,s+1+n,cmp);
	build(1,1,cnt);
	int L=1,R=1,ans=INF;
	while(R<=n)
	{
		while(sum(1)<m&&R<=n)
		{
			change(1,s[R].l,s[R].r,1);
			//put(sum(1));
			++R;
		}
		while(sum(1)>=m)
		{
			ans=min(ans,s[R-1].sum-s[L].sum);
			change(1,s[L].l,s[L].r,-1);
			++L;
		}
	}
	put(ans==INF?-1:ans);
	return 0;
}