Submission #485508

#	Time	Username	Problem	Language	Result	Execution time	Memory
485508		sam571128	Love Polygon (BOI18_polygon)	C++17	46 / 100	714 ms	24244 KiB

polygon

#include <bits/stdc++.h>

#define int long long
#define fastio ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

using namespace std;

const int N = 1e5+5;
int visited[N], arr[N], sz[N];
vector<int> adj[N];

void dfs(int u){
    assert(u <= N);
    assert(!visited[u]);
    sz[u] = 1;
    visited[u] = 1;
    for(auto v : adj[u]){
        if(visited[v]) continue;
        dfs(v);
        sz[u] += sz[v];
    }
}

int idx;
map<string,int> m;

int assign(string x){
    if(m.find(x)==m.end()){
        m[x] = idx++;
    }
    return m[x];
}

signed main(){
    fastio
    int n;
    cin >> n;

    for(int i = 0;i < n;i++){
        string a,b;
        cin >> a >> b;
        int x = assign(a);
        int y = assign(b);
        arr[x] = y;
        adj[x].push_back(y);
        adj[y].push_back(x);
    }

    if(n%2){
        cout << -1 << "\n";
        return 0;
    }

    if(n <= 20){
        int dp[1<<n];
        fill(dp,dp+(1<<n),1e18);
        dp[0] = 0;

        for(int mask = 0;mask < (1<<n); mask++){
            for(int i = 0;i < n;i++){
                if(mask&(1<<i)) continue;
                for(int j = 0;j < n;j++){
                    if(i==j||mask&(1<<j)) continue;
                    dp[mask|(1<<i)|(1<<j)] = min(dp[mask]+(arr[i]!=j)+(arr[j]!=i),dp[mask|(1<<i)|(1<<j)]);
                }
            }
        }

        cout << dp[(1<<n)-1] << "\n";
    }else{
        int ans = 0;
        for(int i = 0;i < n;i++)
            ans += (arr[i] == i);
        for(int i = 0; i < n; i++){
            if(!visited[i]){
                dfs(i); 
                if(sz[i]>2){
                    ans += sz[i]/2; 
                    if(sz[i]%2) ans++;
                }

            }
        }
        cout << max(ans,(int)0) << "\n";
    }
}   

• Subtask 1: 21 / 21
• Subtask 2: 25 / 25
• Subtask 3: 0 / 29
• Subtask 4: 0 / 25