Submission #76851736

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#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for(int i=a;i<n;i++)
typedef long long ll;
const int N=2e5+5;
int n,k;
ll L[N],R[N];
int id[N];
bool check(ll x){
    ll need=max(x,1LL);
    int cnt=0;
    ll last=-4e18;
    rep(i,0,n){
        int j=id[i];
        if(L[j]>=last+need){
            cnt++;
            last=R[j];
            if(cnt>=k) return true;
        }
    }
    return cnt>=k;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>n>>k;
    rep(i,0,n) cin>>L[i]>>R[i];
    rep(i,0,n) id[i]=i;
    sort(id,id+n,[](int a,int b){return R[a]<R[b];});
    if(!check(0)){ cout<<-1<<"\n"; return 0; }
    ll lo=0,hi=1e9,ans=0;
    while(lo<=hi){
        ll mid=(lo+hi)/2;
        if(check(mid)){ ans=mid; lo=mid+1; }
        else hi=mid-1;
    }
    cout<<ans<<"\n";
    return 0;
}
 
 
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#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for(int i=a;i<n;i++)
typedef long long ll;
const int N=2e5+5;
int n,k;
ll L[N],R[N];
int id[N];
bool check(ll x){
    ll need=max(x,1LL);
    int cnt=0;
    ll last=-4e18;
    rep(i,0,n){
        int j=id[i];
        if(L[j]>=last+need){
            cnt++;
            last=R[j];
            if(cnt>=k) return true;
        }
    }
    return cnt>=k;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>n>>k;
    rep(i,0,n) cin>>L[i]>>R[i];
    rep(i,0,n) id[i]=i;
    sort(id,id+n,[](int a,int b){return R[a]<R[b];});
    if(!check(0)){ cout<<-1<<"\n"; return 0; }
    ll lo=0,hi=1e9,ans=0;
    while(lo<=hi){
        ll mid=(lo+hi)/2;
        if(check(mid)){ ans=mid; lo=mid+1; }
        else hi=mid-1;
    }
    cout<<ans<<"\n";
    return 0;
}

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