【牛客】 华华听月月唱歌

原题链接：https://ac.nowcoder.com/acm/contest/392/A

排序后贪心即可， 每次 End = max{r[i]} (l[i] <= End + 1)

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 const int MAX_LEN = 1e5 + 5;
 6 struct section
 7 {
 8     int l, r;
 9 }a[MAX_LEN];
10 int n, m;
11 bool cmp(section a, section b) { return a.l < b.l; }
12 int main()
13 {
14     ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
15     cin >> n >> m;
16     for (int i = 1; i <= m; i++)
17         cin >> a[i].l >> a[i].r;
18     sort(a + 1, a + m + 1, cmp);
19     int end = 0, tot = 0, maxr = 0;
20     for (int i = 1; i <= m; i++)
21         if (a[i].l <= end + 1)
22         {
23             if (a[i].r > maxr)
24                 maxr = a[i].r;
25         }
26         else
27         {
28             end = maxr;
29             maxr = 0;
30             tot++;
31             if (a[i].l <= end + 1)
32             {
33                 if (a[i].r > maxr)
34                     maxr = a[i].r;
35             }
36         }
37     if (end < n && maxr)
38     {
39         end = maxr;
40         tot++;
41     }
42     if (end < n) puts("-1");
43     else cout << tot << endl;
44     
45     return 0;
46 }