Submission #485583

#	Time	Username	Problem	Language	Result	Execution time	Memory
485583		sam571128	Love Polygon (BOI18_polygon)	C++17	100 / 100	248 ms	29788 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 arr[N], dp[N][2], dp2[N][2], dsu[N];
vector<int> adj[N];

int find(int u){
    return dsu[u]==u ? u : dsu[u] = find(dsu[u]);
}

void unite(int u, int v){
    u = find(u), v = find(v);
    if(u==v) return;
    dsu[u] = v;
}


void dfs(int u, int p, int no = -1){
    for(auto v : adj[u]){
        if(v==p) continue;
        dfs(v,u,no);
        dp[u][0] += max(dp[v][0],dp[v][1]);
        dp2[u][0] += max(dp2[v][0],dp2[v][1]);
    }

    for(auto v : adj[u]){
        if(v==p) continue;
        dp[u][1] = max(dp[u][1],dp[u][0]-max(dp[v][0],dp[v][1])+dp[v][0]+1);
        if(v!=no) dp2[u][1] = max(dp2[u][1],dp2[u][0]-max(dp2[v][0],dp2[v][1])+dp2[v][0]+1);
    }

    if(u==no) dp2[u][1] = -1e18;
}

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
    iota(dsu,dsu+N,0);
    int n;
    cin >> n;

    vector<pair<int,int>> edges;
    for(int i = 0;i < n;i++){
        string a,b;
        cin >> a >> b;
        int x = assign(a);
        int y = assign(b);
        arr[x] = y;
        if(find(x)!=find(y)) unite(x,y), adj[x].push_back(y), adj[y].push_back(x);
        else edges.push_back({y,x});
    }

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


    int ans = n;

    for(auto [x,y] : edges){
        dfs(x,x,y);
        if(x!=y) ans -= max({dp[x][0],dp[x][1],dp2[x][0]+(arr[x]==y && arr[y]==x ? 2 : 1)});
        else ans -= max(dp[x][0],dp[x][1]);
    }
    


    cout << ans << "\n";
}   

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