Submission #1053463

#	Time	Username	Problem	Language	Result	Execution time	Memory
1053463		steveonalex	Mousetrap (CEOI17_mousetrap)	C++17	100 / 100	457 ms	207540 KiB

mousetrap

#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
 
#define MASK(i) (1LL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
#define ALL(v) (v).begin(), (v).end()
#define block_of_code if(true)
 
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll gcd(ll a, ll b){return __gcd(a, b);}
ll lcm(ll a, ll b){return a / gcd(a, b) * b;}
 
ll LASTBIT(ll mask){return (mask) & (-mask);}
int pop_cnt(ll mask){return __builtin_popcountll(mask);}
int ctz(ull mask){return __builtin_ctzll(mask);}
int logOf(ull mask){return 63 - __builtin_clzll(mask);}
 
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rngesus(ll l, ll r){return l + (ull) rng() % (r - l + 1);}
 
template <class T1, class T2>
    bool maximize(T1 &a, T2 b){
        if (a < b) {a = b; return true;}
        return false;
    }
 
template <class T1, class T2>
    bool minimize(T1 &a, T2 b){
        if (a > b) {a = b; return true;}
        return false;
    }
 
template <class T>
    void printArr(T container, string separator = " ", string finish = "\n", ostream &out = cout){
        for(auto item: container) out << item << separator;
        out << finish;
    }
 
template <class T>
    void remove_dup(vector<T> &a){
        sort(ALL(a));
        a.resize(unique(ALL(a)) - a.begin());
    }

const int N = 1e6 + 69;
int n, s, t;
vector<int> graph[N], val[N];
int dp[N];
int parent[N];

bool find_t(int u, int p){
    parent[u] = p;
    if (u == t) return true;
    bool check = false;
    for(int v: graph[u]) if (v != p) 
        check = check || find_t(v, u);
    return check;
}

void dfs(int u, int p){
    int child_cnt = 0;
    for(int v: graph[u]) if (v != p) {
        dfs(v, u);
        child_cnt++;
    }
    if (child_cnt <= 1){
        dp[u] = child_cnt;
        return;
    }
    vector<int> toxic;
    for(int v: graph[u]) if (v != p) toxic.push_back(dp[v]);
    sort(ALL(toxic), greater<int>());
    dp[u] = toxic[1] + toxic.size();
}

int main(void){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
 
    clock_t start = clock();

    cin >> n >> s >> t;
    if (s == t){
        cout << 0 << "\n";
        return 0;
    }
    for(int i = 1; i<n; ++i){
        int u, v; cin >> u >> v;
        graph[u].push_back(v);
        graph[v].push_back(u);
    }

    int branch = -1;
    for(int v: graph[s]){
        if (find_t(v, s)) branch = v;
    }
    graph[s] = {branch};

    int u = t;

    vector<int> chain;

    while(u != s){
        dfs(u, parent[u]);
        for(int v: graph[u]) if (v != parent[u]) val[u].push_back(dp[v]);
        sort(ALL(val[u]), greater<int>());

        auto it = find(ALL(graph[parent[u]]), u);
        graph[parent[u]].erase(it);

        chain.push_back(u);

        u = parent[u];
    }

    int sum = 0;
    for(int i: chain){
        sum += val[i].size();
    }

    int l = 0, r = n * 2;
    while(l < r){
        int mid = (l + r) >> 1;

        // cout << "Mid: " << mid << "\n";

        int _s = sum;
        vector<int> b;

        for(int i = 0; i < chain.size(); ++i){
            int u = chain[i];
            for(int v: val[u]) {
                if (v + _s + b.size() > mid)
                    b.push_back(i);
                _s--;
            }
        }

        bool legit = true;
        if (b.size() > min(chain.size(), mid)) legit = false;
        if (legit){
            for(int i = 0; i < b.size(); ++i) if (b[i] < i) legit = false;
        }
        if (legit) r = mid;
        else l = mid + 1;
    }

    cout << l << "\n";





    cerr << "Time elapsed: " << clock() - start << " ms!\n";
    return 0;
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:134:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  134 |         for(int i = 0; i < chain.size(); ++i){
      |                        ~~^~~~~~~~~~~~~~
mousetrap.cpp:137:39: warning: comparison of integer expressions of different signedness: 'std::vector<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
  137 |                 if (v + _s + b.size() > mid)
      |                     ~~~~~~~~~~~~~~~~~~^~~~~
mousetrap.cpp:144:22: warning: comparison of integer expressions of different signedness: 'std::vector<int>::size_type' {aka 'long unsigned int'} and 'll' {aka 'long long int'} [-Wsign-compare]
  144 |         if (b.size() > min(chain.size(), mid)) legit = false;
      |             ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:146:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  146 |             for(int i = 0; i < b.size(); ++i) if (b[i] < i) legit = false;
      |                            ~~^~~~~~~~~~

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