不相交可以转化最长上升子序列问题

#include <iostream>
#include <algorithm>

using namespace std;
typedef pair<int, int> PII;
const int N = 5e3 + 10;
PII a[N];
int f[N];

int main() {
    int n;
    cin >> n;
    for(int i = 0; i < n; i++) cin >> a[i].first >> a[i].second;
    sort(a, a + n);
    int ans = 0;
    for(int i = 0; i < n; i++) {
        f[i] = 1;
        for(int j = 0; j < i; j++) if(a[j].second < a[i].second) f[i] = max(f[i], f[j] + 1);
        ans = max(ans, f[i]);
    }
    cout << ans;
    return 0;
}