BZOJ 5102: [POI2018]Prawnicy

考虑最优解的集合中一定有一个$l$最大的，我们就去枚举左端点，把所有$l$小于等于它的全丢进堆里，取前$k$个即可。

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

 #define N 1000010
 #define fi first
 #define se second
 #define pii pair <int, int>
 int n, k;
 struct node
 {
     int l, r, id;
     void scan(int _id)
     {
         id = _id;
         scanf("%d%d", &l, &r);
     }
     bool operator < (const node &other) const
     {
         return l < other.l;
     }
 }a[N];

 void work()
 {
     priority_queue <pii, vector <pii>, greater <pii> > pq;
     int Max = , L = -, R = -;
     for (int i = ; i <= n; ++i)
     {
         pq.push(pii(a[i].r, a[i].id));
         if ((int)pq.size() > k)
             pq.pop();
         if ((int)pq.size() == k)
         {
             int t = max(, pq.top().first - a[i].l);
             if (t > Max)
             {
                 Max = t;
                 L = a[i].l;
                 R = pq.top().fi;
             }
         }
     }
     printf("%d\n", Max);
     for (int i = ; i <= n; ++i)
     {
         if (a[i].l <= L && a[i].r >= R)
         {
             printf("%d", a[i].id);
             if (k == )
             {
                 puts("");
                 return;
             }
             else
             {
                 --k;
                 putchar(' ');
             }
         }
     }
 }

 void Run()
 {
     while (scanf("%d%d", &n, &k) != EOF)
     {
         for (int i = ; i <= n; ++i)
             a[i].scan(i);
         sort(a + , a +  + n);
         work();
     }
 }

 int main()
 {
     #ifdef LOCAL
         freopen("Test.in", "r", stdin);
     #endif 

     Run();
     return ;
 }