$n^2$ 肯定过不了，只要比较左边与最右边就行了。
```cpp
#include<iostream>
#include<cstring>
#include<string>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
const int MAX = 1e6 + 10 ;
struct node{
int left ;
int right ;
}no[MAX];
bool cmp ( node a , node b ){
return a.right < b.right ;
}
int main()
{
int n;
int ans = 0 , the_rightest = -1 ;
scanf( "%d" , &n );
for (int i = 1 ; i <= n ; i ++){
scanf( "%d %d" , &no[i].left , &no[i].right );
}
sort (no + 1 , no+ n + 1 , cmp);
for (int i = 1 ; i <= n ; i++){
if( no[i].left < the_rightest ) continue;
ans++ ;
the_rightest = no[i].right ;
}
cout << ans ;
return 0;
}
```
by lhz123bc @ 2024-03-24 17:32:29