[POI 2018] Prawnicy

#include<bits/stdc++.h>
using namespace std;
#define MAXN 1000010

struct segment
{
        int id;
        int l,r;
} a[MAXN];

int n,k,ans,l,r,len;
priority_queue< pair<int,int> > q;
int res[MAXN];

template <typename T> inline void read(T &x)
{
    int f = 1; x = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) if (c == ‘-‘) f = -f; 
    for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - ‘0‘;
    x *= f;
}
inline bool cmp(segment a,segment b)
{
        if (a.l == b.l) return a.r > b.r;
        else return a.l < b.l;
}

int main() 
{
        
        read(n); read(k);
        for (int i = 1; i <= n; i++) 
        {
                a[i].id = i;
                read(a[i].l);
                read(a[i].r);        
        }
        sort(a + 1,a + n + 1,cmp);
        ans = 0;
        for (int i = 1; i <= n; i++)
        {
                if ((int)q.size() < k) 
                {
                        q.push(make_pair(-a[i].r,a[i].id));
                        if ((int)q.size() == k) 
                        {
                                ans = max(ans,-q.top().first - a[i].l);
                                l = a[i].l; r = -q.top().first;
                                continue;
                        }
                } else
                {
                        if (a[i].r < -q.top().first) continue;
                        pair<int,int> tmp = q.top();
                        q.pop();
                        q.push(make_pair(-a[i].r,a[i].id));
                        if (-q.top().first - a[i].l > ans)
                        {
                                ans = -q.top().first - a[i].l;
                                l = a[i].l; r = -q.top().first;
                        }
                }    
        }
        printf("%d\n",ans);
        if (ans == 0)
        {
                for (int i = 1; i <= k; i++)
                        printf("%d ",i);
                printf("\n");
                return 0;
        }
        for (int i = 1; i <= n; i++)
        {
                if (a[i].l <= l && a[i].r >= r)
                {
                        res[++len] = a[i].id;
                        if ((--k) == 0) break;
                }
        }
        for (int i = 1; i <= len; i++) printf("%d ",res[i]);
        printf("\n");
        
        return 0;
    
}