题目链接:点击这里
思路:将南岸的城市从小到大排序,那么北岸的不相交的友好城市就是上升子序列。
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
const int N = 5050;
typedef pair<int,int> PII;
vector<PII> a;
int n, f[N];
int main()
{
scanf("%d", &n);
a.push_back({-1, -1});
for(int i = 1; i <= n; ++i)
{
int x, y;
scanf("%d%d", &x, &y);
a.push_back({x, y});
}
sort(a.begin(), a.end());
for(int i = 1; i <= n; ++i)
{
f[i] = 1;
for(int j = 1; j < i; ++j)
if(a[j].second < a[i].second) f[i] = max(f[i], f[j] + 1);
}
int ans = -1;
for(int i = 1; i <= n; ++i)
ans = max(ans, f[i]);
printf("%d\n", ans);
return 0;
}