题解 | 小红的不动点分配

#include <bits/stdc++.h>
using namespace std;

map<int, int>mp;
int main() {
    int n;
    cin >> n;
    vector<int>a(2 * n + 1);
    for (int i = 1; i <= 2 * n; i++){
        cin >> a[i];
    }

    for (int i = 1; i <= 2 * n; i++){
        if (a[i] <= n)mp[a[i]]++;  
    }
    int ans = 0;
    for(auto asd: mp){
        if (asd.second <= 2)ans += asd.second;
        else ans += 2;
    }
    cout << ans;
}