tyvj1213 嵌套矩形

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#include<vector>
#define ll long long
using namespace std;
const int maxn = 2005;
vector<int> g[maxn];
int n,a[maxn],b[maxn],topo[maxn],cnt;
int f[maxn],ans;
bool vis[maxn];
void dfs(int x){
    vis[x] = true;
    for(int i = 0;i < g[x].size();i++){
        if(!vis[g[x][i]]) dfs(g[x][i]);
    }
    topo[cnt--] = x;
}
void dp(int x){
    if(!g[x].size()){
        f[x] = 1;
        return;
    }
    for(int i = 0;i < g[x].size();i++){
        if(!f[g[x][i]]) dp(g[x][i]);
        f[x] = max(f[x],f[g[x][i]] + 1);
    }
    ans = max(f[x],ans);
}
int main(){
    cin>>n;
    for(int i = 1;i <= n;i++){
        scanf("%d%d",&a[i],&b[i]);
        if(a[i] < b[i]) swap(a[i],b[i]);
    }
    for(int i = 1;i <= n;i++){
        for(int j = i+1;j <= n;j++){
            if(a[i] > a[j] && b[i] > b[j]) g[i].push_back(j);
            else if(a[j] > a[i] && b[j] > b[i]) g[j].push_back(i);
        }
    }
    cnt = n;
    for(int i = 1;i <= n;i++){
        if(!vis[i]) dfs(i);
    }
    for(int i = 1;i <= n;i++){
        if(!f[topo[i]]) dp(topo[i]); 
    }
    cout<<ans;
    return 0;
}