题解 | 小红的不动点分配

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define quick ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
const int inf = 0x3f3f3f3f, maxn = 2e5 + 5, mod = 998244353;
inline int read() {
    int s = 0, w = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')w = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')s = s * 10 + ch - '0', ch = getchar();
    return s * w;
}
void solve() {
    int n;n=read();
    vector<int>arr(n+1);
    for(int i=1,tmp;i<=2*n;i++){
        cin>>tmp;
        if(tmp>n) continue;
        arr[tmp]++;
    }
    int ans=0;
    for(int i=1;i<=n;i++){
        if(arr[i]>=2){
            ans+=2;
        }else if(arr[i]==1){
            ans++;
        }
    }
    cout<<ans<<endl;
}
signed main() {
    int t = 1;
//  cin>>t;
    while (t--) {
        solve();
    }
    return 0;
}