[CF754D] Fedor and coupons - 贪心,堆

Description

给出n个区间，要求选出k个区间，是k个区间的并尽可能大

Solution

按 l 排序后顺序扫描，用一个堆维护 l 不超过当前的，最大的 k 个 r

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

#define int long long
const int N = 1e6 + 5;
int n, k;

struct Node
{
    int l, r, id;

    bool operator<(const Node &rhs)
    {
        return l < rhs.l;
    }
} a[N];

signed main()
{
    ios::sync_with_stdio(false);

    cin >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i].l >> a[i].r;
        a[i].id = i;
    }

    sort(a + 1, a + n + 1);

    int ans = 0, ansx = 0;

    priority_queue<int, vector<int>, greater<int>> que;
    for (int i = 1; i <= n; i++)
    {
        que.push(a[i].r);
        while (que.size() > k)
            que.pop();
        if (que.size() == k)
        {
            if (que.top() - a[i].l + 1 > ans)
            {
                ans = que.top() - a[i].l + 1;
                ansx = a[i].l;
            }
        }
    }

    int left = ansx, right = ansx + ans - 1;
    if (right < left)
        right = -2e9, left = 2e9;

    vector<int> res;
    for (int i = 1; i <= n; i++)
        if (a[i].l <= left && a[i].r >= right)
            res.push_back(a[i].id);

    cout << ans << endl;
    for (int i = 0; i < k; i++)
        cout << res[i] << " ";
    cout << endl;
}