Submission #47084

#	Time	Username	Problem	Language	Result	Execution time	Memory
47084		qoo2p5	Mousetrap (CEOI17_mousetrap)	C++17	100 / 100	1190 ms	230704 KiB

mousetrap

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int INF = (int) 1e9 + 1e6;
const ll LINF = (ll) 1e18 + 1e9;
const ll MOD = (ll) 1e9 + 7;

#define sz(x) (int) (x).size()
#define mp(x, y) make_pair(x, y)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define lb(s, t, x) (int) (lower_bound(s, t, x) - s)
#define ub(s, t, x) (int) (upper_bound(s, t, x) - s)
#define rep(i, f, t) for (auto i = f; i < t; ++(i))
#define per(i, f, t) for (auto i = (f); i >= (t); --(i))

ll power(ll x, ll y, ll mod = MOD) {
    if (y == 0) {
        return 1;
    }
    if (y & 1) {
        return power(x, y - 1, mod) * x % mod;
    } else {
        ll tmp = power(x, y / 2, mod);
        return tmp * tmp % mod;
    }
}

template<typename A, typename B> bool mini(A &x, const B &y) {
    if (y < x) {
        x = y;
        return true;
    }
    return false;
}

template<typename A, typename B> bool maxi(A &x, const B &y) {
    if (x < y) {
        x = y;
        return true;
    }
    return false;
}

void add(ll &x, ll y) {
    x += y;
    if (x >= MOD) x -= MOD;
    if (x < 0) x += MOD;
}

void run();

#define TASK ""

int main() {
#ifdef LOCAL
    if (strlen(TASK) > 0) {
        cerr << "Reminder: you are using file i/o, filename: " TASK "!" << endl << endl;
    }
#endif
#ifndef LOCAL
    if (strlen(TASK)) {
        freopen(TASK ".in", "r", stdin);
        freopen(TASK ".out", "w", stdout);
    }
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
#endif
    cout << fixed << setprecision(12);
    run();
    return 0;
}

// == SOLUTION == //

const int N = (int) 1e6 + 123;

int n, t, m;
vector<int> g[N];
int p[N];
int cost[N];
int up[N];

void calc(int v, int p = -1) {
    ::p[v] = p;
    int ptr = 0;
    int pos = -1;
    
    for (int u : g[v]) {
        if (u == p) {
            pos = ptr;
            continue;
        }
        
        up[u] = up[v];
        if (v != t) {
            up[u] += sz(g[v]) - 2;
        }
        calc(u, v);
        ptr++;
    }
    
    if (pos != -1) {
        g[v].erase(g[v].begin() + pos);
    }
    
    if (sz(g[v]) == 0) {
        cost[v] = 0;
    } else if (sz(g[v]) == 1) {
        cost[v] = 1;
    } else {
        vector<int> q;
        for (int u : g[v]) {
            q.push_back(cost[u]);
        }
        sort(all(q));
        cost[v] = sz(g[v]) + q[sz(q) - 2];
    }
}

void run() {
    cin >> n >> t >> m;
    rep(i, 0, n - 1) {
        int u, v;
        cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }
    
    calc(t);
    vector<pair<int, int>> wow;
    int prv = -1;
    int w = m;
    int dist = 0;
    while (w != t) {
        for (int u : g[w]) {
            if (u == prv) {
                continue;
            }
            wow.pb({dist + 1, cost[u] + up[u] + (dist == 0)});
        }
        prv = w;
        w = p[w];
        dist++;
    }
    
    sort(all(wow));
    
    int left = -1;
    int right = n;
    while (right - left > 1) {
        int mid = (left + right) / 2;
        bool ok = 1;
        int cnt = 0;
        rep(i, 0, sz(wow)) {
            int j = i;
            while (j + 1 < sz(wow) && wow[j + 1].first == wow[j].first) {
                j++;
            }
            int ncnt = cnt;
            
            rep(k, i, j + 1) {
                auto it = wow[k];
                if (it.second + cnt <= mid) {
                    continue;
                }
                if (ncnt >= it.first) {
                    ok = 0;
                    break;
                }
                ncnt++;
            }
            
            cnt = ncnt;
            i = j;
        }
        
        ok &= (cnt <= mid);
        
        if (ok) {
            right = mid;
        } else {
            left = mid;
        }
    }
    
    cout << right << "\n";
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:67:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
         freopen(TASK ".in", "r", stdin);
         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:68:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
         freopen(TASK ".out", "w", stdout);
         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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