Submission #468198

#	Time	Username	Problem	Language	Result	Execution time	Memory
468198		idk321	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	363 ms	62832 KiB

mousetrap

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

const int N = 1000005;
vector<int> adj[N];
int upCost[N];
int downCost[N];
int p[N];
vector<vector<int>> sideNodes;

int n, t, m;

void dfs(int node, int par) {
    p[node] = par;
    for (int next : adj[node]) {
        if (next == par) continue;
        dfs(next, node);
    }
}

void calcDown(int node, int depth) {
    if (adj[node].size() == 1) {
        downCost[node] = depth;
        return;
    }
    if (adj[node].size() == 2) {
        downCost[node] = depth + 1;
        return;
    }

    array<int, 2> most{0, 0};
    for (int next : adj[node]) {
        if (next == p[node]) continue;
        calcDown(next, depth + 1);
        if (downCost[next] > most[1]) most[1] = downCost[next];
        if (most[0] < most[1]) swap(most[0], most[1]);
    }

    downCost[node] = adj[node].size() - 2 + most[1];
}

void goUp(int node, int prev = -1) {
    if (node == t) return;
    if (prev != -1)upCost[node] = adj[node].size() - 2;
    else upCost[node] = adj[node].size() - 1;
    goUp(p[node], node);
    upCost[node] += upCost[p[node]];
    vector<int> curSideNodes;
    for (int next : adj[node]) {
        if (next == prev || next == p[node]) continue;
        curSideNodes.push_back(next);
        upCost[next] = upCost[node] - 1;
        calcDown(next, 1);
    }
    sideNodes.push_back(curSideNodes);
    sort(sideNodes.rbegin(), sideNodes.rend());
}



bool poss(int most) {
    int already = 0;
    int canHave = 1;
    for (vector<int>& nodesVector : sideNodes) {
        int exactlyMost = 0;
        int moreThanMost = 0;
        for (int i : nodesVector) {
            if (already + downCost[i] + upCost[i] > most) {
                if (already < canHave) already++;
                else return false;
            }
        }
        canHave++;
    }

    return true;
}


int bs() {
    int a = 0;
    int b = 2 * n;
    int res = -1;
    while (a <= b) {

        int mid =(a +b ) / 2;
        //cout << a<< " " << b << " "<< mid << " " << poss(mid) << "\n";
        if (poss(mid)) {
            res = mid;
            b = mid - 1;
        } else a = mid + 1;
    }

    return res;
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    cin >> n >> t >> m;

    for (int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    dfs(t, -1);
    goUp(m);

    cout << bs() << "\n";
}

/*
10 1 2
1 2
2 3
2 4
3 9
3 5
4 7
4 6
6 8
7 10
*/

Compilation message (stderr)

mousetrap.cpp: In function 'bool poss(int)':
mousetrap.cpp:67:13: warning: unused variable 'exactlyMost' [-Wunused-variable]
   67 |         int exactlyMost = 0;
      |             ^~~~~~~~~~~
mousetrap.cpp:68:13: warning: unused variable 'moreThanMost' [-Wunused-variable]
   68 |         int moreThanMost = 0;
      |             ^~~~~~~~~~~~

• Subtask 1: 0 / 20
• Subtask 2: 0 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35