Submission #1273568

#	Time	Username	Problem	Language	Result	Execution time	Memory
1273568		KindaGoodGames	The Xana coup (BOI21_xanadu)	C++20	100 / 100	110 ms	44400 KiB

xanadu

#include<bits/stdc++.h>

using namespace std;

#define int long long
vector<vector<int>> adj;
vector<vector<vector<int>>> dp;  
// int INF = numeric_limits<int>::max()/8;
int INF = 2e5;
    int r = -1;
    vector<bool> ostate;

int determine(priority_queue<int,vector<int>,greater<int>>& delta, int s){
    int mi = s; 
    while(delta.size() >= 2 && delta.top() < 0){
        s += delta.top();
        delta.pop();
        s += delta.top();
        delta.pop();
        mi = min(mi,s);
    }
    return mi;
}
void clearpq(priority_queue<int,vector<int>,greater<int>>& pq){
    while(pq.size()) pq.pop();
}
void DFS(int v, int p){
    // if v is a leaf, then not doing anything will cause the node to be in the same state or flipping it will cause it to go to the other state
    // no other dp-state can be reached
    if(v != r && adj[v].size() == 1){
        dp[v][ostate[v]][0] = 0; 
        dp[v][!ostate[v]][1] = 1; 
        return;
    }

    vector<int> child;
    for(auto u : adj[v]){
        if(u == p) continue;
        DFS(u,v);
        child.push_back(u);
    }

    if(child.size() == 1){
        int a = child[0];
        dp[v][ostate[v]][0] = dp[a][1][0];
        dp[v][!ostate[v]][0] = dp[a][1][1];
        
        dp[v][!ostate[v]][1] = dp[a][0][0]+1;
        dp[v][ostate[v]][1] = dp[a][0][1]+1;
    }else{
        // no change, no ops
        int s = 0;
        priority_queue<int,vector<int>,greater<int>> delta;
        for(auto c : child){
            s += dp[c][1][0];
            delta.push(dp[c][1][1]-dp[c][1][0]);
        }  
        dp[v][ostate[v]][0] = determine(delta,s);
        clearpq(delta); s = 0; 

        // change, no ops 
        for(auto c : child){
            s += dp[c][1][0];
            delta.push(dp[c][1][1]-dp[c][1][0]);
        }  
        s += delta.top(); delta.pop();
        dp[v][!ostate[v]][0] = determine(delta,s);
        clearpq(delta); s = 0;  
        
        // no change, ops 
        for(auto c : child){
            s += dp[c][0][0];
            delta.push(dp[c][0][1]-dp[c][0][0]);
        }  
        dp[v][!ostate[v]][1] = determine(delta,s)+1;
        clearpq(delta); s = 0; 

        // change, ops 
        for(auto c : child){
            s += dp[c][0][0];
            delta.push(dp[c][0][1]-dp[c][0][0]);
        }  
        s += delta.top(); delta.pop();
        dp[v][ostate[v]][1] = determine(delta,s)+1;
        clearpq(delta); s = 0;   
    }
    cerr <<"";
}

int32_t main(){
    int n;
    cin >> n;
    adj.resize(n);
    dp = vector<vector<vector<int>>>(n, vector<vector<int>>(2, vector<int>(2,INF)));
    for(int i = 0; i < n-1LL; i++){
        int a,b;
        cin >> a >> b;
        a--;b--;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }

    ostate.resize(n);
    for(int i = 0; i < n; i++){
        int a;
        cin >> a;
        ostate[i] = a;
        ostate[i] = !ostate[i];
    }

    for(int i = 0; i < n; i++){
        if(adj[i].size() <= 2) {
            r = i;
            break;
        }
    }

    DFS(r,r);
    
    int ans = min({dp[r][1][0],dp[r][1][1]});
    if(ans >= INF){
        cout << "impossible\n";
        return 0;
    }

    cout << ans << endl;
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30