友好城市（LIS+结构体排序）

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cmath>
 4 #include <algorithm>
 5 #include <bits/stdc++.h>
 6 using namespace std;
 7 typedef long long ll;
 8 const int maxn = 5010;
 9 
10 int dp[maxn];
11 struct node{
12     int north;
13     int south;
14 }a[maxn];
15 
16 bool cmp(node a, node b){
17     return a.north<b.north;
18 }
19 
20 int main()
21 {
22     int n,maxx=0;
23     scanf("%d",&n);
24     for(int i=0;i<n;i++){
25         scanf("%d %d",&a[i].south, &a[i].north);
26     }
27     sort(a,a+n,cmp);
28     for(int i=0;i<n;i++){
29         for(int j=0;j<i;j++){
30             if( a[i].south>a[j].south ){
31                 dp[i] = max(dp[j]+1,dp[i]);
32                 maxx = max(maxx,dp[i]);
33             }
34         }
35     }
36     printf("%d\n",maxx+1);
37     return 0;
38 }