求助：不知为何60分

#include <cstdio>
#include <map>
#include <iostream>
#include <algorithm>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;

const int maxn = 8e5 + 5;
const int mod = 1e9 + 7;

int n, m, k;

struct Line {
  int h, pos, id;
  Line(int h = 0, int pos = 0, int id = 0):
      h(h), pos(pos), id(id) {};
};

Line a[maxn];

bool cmp(Line a, Line b) {
  return (a.pos == b.pos) ? a.h > b.h : a.pos < b.pos;
}

map<int, int> mp;
map<int, int>::iterator it;
bool vis[maxn];
pair<int, int> ans[maxn];

int main() {
  scanf("%d", &n); 
  int h, l, r;
  for (int i = 1; i <= n; i++) {
    scanf("%d%d%d", &h, &l, &r);
    a[i * 2 - 1] = Line(h, l, i);
    a[i * 2] = Line(h, r, i);
  }
  sort(a + 1, a + 2 * n + 1, cmp);
  int cur = 0;
  int top = 0;
  for (int i = 1; i <= 2 * n; i++) {
    if (vis[a[i].id]) {
      mp[a[i].h]--;
      if (mp[a[i].h] == 0) {
        mp.erase(a[i].h);
      }
    } else {
      vis[a[i].id] = 1;
      mp[a[i].h]++;
    }
    if (mp.size() == 0) {
      ans[++top] = (make_pair(a[i].pos, cur));
      cur = 0;
      ans[++top] = (make_pair(a[i].pos, cur));
      continue;
    }
    it = --mp.end();
    if (cur != it->first) {
      ans[++top] = (make_pair(a[i].pos, cur));
      cur = it->first;
      ans[++top] = (make_pair(a[i].pos, cur));
    }
  }
  printf("%d\n", top);
  for (int i = 1; i <= top; i++) {
    printf("%d %d\n", ans[i].first, ans[i].second);
  }
  return 0;
}