Submission #143514

#	Time	Username	Problem	Language	Result	Execution time	Memory
143514		popovicirobert	Mousetrap (CEOI17_mousetrap)	C++14	45 / 100	1097 ms	75996 KiB

mousetrap

#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long



/*const int MOD = ;

inline int lgput(int a, int b) {
    int ans = 1;
    while(b > 0) {
        if(b & 1) ans = (1LL * ans * a) % MOD;
        b >>= 1;
        a = (1LL * a * a) % MOD;
    }
    return ans;
}

inline void mod(int &x) {
    if(x >= MOD)
        x -= MOD;
}

inline void add(int &x, int y) {
    x += y;
    mod(x);
}

inline void sub(int &x, int y) {
    x += MOD - y;
    mod(x);
}

inline void mul(int &x, int y) {
    x = (1LL * x * y) % MOD;
}

inline int inv(int x) {
    return lgput(x, MOD - 2);
}*/

/*int fact[], invfact[];

inline void prec(int n) {
    fact[0] = 1;
    for(int i = 1; i <= n; i++) {
        fact[i] = (1LL * fact[i - 1] * i) % MOD;
    }
    invfact[n] = lgput(fact[n], MOD - 2);
    for(int i = n - 1; i >= 0; i--) {
        invfact[i] = (1LL * invfact[i + 1] * (i + 1)) % MOD;
    }
}

inline int comb(int n, int k) {
    if(n < k) return 0;
    return (1LL * fact[n] * (1LL * invfact[k] * invfact[n - k] % MOD)) % MOD;
}*/

using namespace std;

const int MAXN = (int) 1e6;

vector <int> g[MAXN + 1];
int father[MAXN + 1], lvl[MAXN + 1];

void dfs(int nod, int par) {
    father[nod] = par;
    lvl[nod] = lvl[par] + 1;
    for(auto it : g[nod]) {
        if(it != par) {
            dfs(it, nod);
        }
    }
}

int dp[MAXN + 1];
bool vis[MAXN + 1];

inline void combine(pair <int, int> &mx, int cur) {
    if(mx.first < cur) {
        mx.second = mx.first;
        mx.first = cur;
    }
    else if(mx.second < cur) {
        mx.second = cur;
    }
}

void go(int nod, int par, int sum) {
    int sz = (int) g[nod].size() - 1;
    pair <int, int> mx = {0, 0};
    for(auto it : g[nod]) {
        if(it != par) {
            go(it, nod, sum + sz - vis[nod]);
            combine(mx, dp[it]);
        }
    }
    if(sz > 1) {
        dp[nod] = mx.second;
    }
    else {
         dp[nod] = sz - vis[nod] + sum;
    }
}

int main() {
#if 0
    ifstream cin("A.in");
    ofstream cout("A.out");
#endif
    int i, n, t, m;
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    cin >> n >> t >> m;

    if(m == t) {
        cout << 0;
        return 0;
    }

    for(i = 1; i < n; i++) {
        int x, y;
        cin >> x >> y;
        g[x].push_back(y);
        g[y].push_back(x);
    }

    dfs(t, 0);

    int nod = m, dst = 1;
    vector < pair <int, int> > nodes; nodes.push_back({m, 0});

    while(father[nod] != t) {
        dst++;
        for(auto it : g[father[nod]]) {
            if(it != nod && lvl[it] == lvl[nod]) {
                nodes.push_back({it, dst});
            }
        }
        nod = father[nod];
        vis[nod] = 1;
    }
    go(nod, t, 0);

    auto check = [&](int X) -> bool {
        int cnt = 0;
        for(auto it : nodes) {
            if(dp[it.first] + cnt > X) {
                cnt++;
            }
            if(cnt > it.second) {
                return 0;
            }
        }
        return cnt <= X;
    };

    int res = -1;
    for(int step = 1 << 20; step; step >>= 1) {
        if(check(res + step) == 0) {
            res += step;
        }
    }

    cout << res + 1;

    return 0;
}

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