Submission #571595

#	Time	Username	Problem	Language	Result	Execution time	Memory
571595		piOOE	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	794 ms	85992 KiB

mousetrap

#include <bits/stdc++.h>

using namespace std;

#define sz(x) ((int)size(x))
#define all(x) begin(x), end(x)
#define trace(x) cout << #x << ": " << (x) << endl;

typedef long long ll;

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

int rand(int l, int r) { return (int) ((ll) rnd() % (r - l + 1)) + l; }

template<typename T>
bool ckmn(T &x, T y) {
    if (x > y) {
        x = y;
        return true;
    }
    return false;
}

template<typename T>
bool ckmx(T &x, T y) {
    if (x < y) {
        x = y;
        return true;
    }
    return false;
}

const int N = 1000001, infI = 1e9 + 7;
const ll infL = 3e18;

int n, t, m;
vector<int> g[N];
int dp[N], parent[N], depth[N], deg[N], gg[N], sum_deg[N];
vector<int> tops;

void dfs(int v, int p) {
    parent[v] = p;
    int mx1 = 0, mx2 = 0;
    deg[v] = (p == v ? sz(g[v]) : sz(g[v]) - 1);
    sum_deg[v] = sum_deg[p] + (p == v ? 1 : deg[v]);
    for (int to: g[v]) {
        if (to != p) {
            depth[to] = depth[v] + 1;
            dfs(to, v);
            if (mx1 < dp[to]) {
                mx2 = mx1;
                mx1 = dp[to];
            } else if (mx2 < dp[to]) {
                mx2 = dp[to];
            }
        }
    }
    dp[v] = mx2 + deg[v];
    tops.push_back(v);
}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    auto smart_solve = [&]() -> int {
        int ans = infI;
        int l = infI, r = 3 * n;
        int cnt = 0;
        for (int i = 0; i < n; ++i) {
            if (gg[i] != -1) {
                l = min(l, gg[i]);
                ++cnt;
            }
        }
        if (l == infI) {
            return 0;
        }
        if (cnt == 1) {
            return 1;
        }
        l -= 1;
        while (l + 1 < r) {
            int mid = (l + r) >> 1;
            vector<int> pos;
            vector<bool> used(n);
            for (int x: tops) {
                if (gg[x] > mid) {
                    pos.push_back(x);
                }
            }
            int x = m;
            int pnt = 0;
            bool ok = true;
            while (x != t) {
                if (pnt < sz(pos)) {
                    used[pos[pnt++]] = true;
                }
                for (int to: g[x]) {
                    if (to != parent[x] && gg[to] > mid && !used[to]) {
                        ok = false;
                        break;
                    }
                }
                if (!ok) {
                    break;
                }
                x = parent[x];
            }
            if (ok) {
                ans = min(ans, mid);
                r = mid;
            } else {
                l = mid;
            }
        }
        return ans;
    };
    auto not_very_smart_solve = [&]() -> int {
        int ans = infI;
        int l = infI;
        int cnt = 0;
        for (int i = 0; i < n; ++i) {
            if (gg[i] != -1) {
                l = min(l, gg[i]);
                ++cnt;
                assert(gg[i] <= 3 * n);
            }
        }
        if (l == infI) {
            return 0;
        }
        if (cnt == 1) {
            return 1;
        }
        for (int mid = l; mid <= 3 * n; ++mid) {
            vector<int> pos;
            vector<bool> used(n);
            for (int x: tops) {
                if (gg[x] > mid) {
                    pos.push_back(x);
                }
            }
            int x = m;
            int pnt = 0;
            bool ok = true;
            while (x != t) {
                if (pnt < sz(pos)) {
                    used[pos[pnt++]] = true;
                }
                for (int to: g[x]) {
                    if (to != parent[x] && gg[to] > mid && !used[to]) {
                        ok = false;
                        break;
                    }
                }
                if (!ok) {
                    break;
                }
                x = parent[x];
            }
            if (ok) {
                ans = min(ans, mid);
            }
        }
        return ans;
    };

    auto stupid_solve= [&]() -> int {
        int ans = infI;
        vector<int> pos;
        for (int i = 0; i < n; ++i) {
            if (gg[i] != -1)
                pos.push_back(i);
        }
        if (sz(pos) == 1)
            return 1;
        if (pos.empty())
            return 0;
        do {
            vector<bool> used(n);
            int x = m;
            int prv = -1;
            int pnt = 0;
            while (x != t) {
                if (pnt < sz(pos))
                    used[pos[pnt++]] = true;
                for (int to : g[x]) {
                    if (to != parent[x] && prv != to && !used[to]) {
                        int now = dp[to] + 1;
                        int pp = prv;
                        for (int z = x; z != t; z = parent[z]) {
                            for (int uu : g[z]) {
                                if (!used[uu] && pp != uu & to != uu && uu != parent[z])
                                    ++now;
                            }
                            pp = z;
                        }
                        now += pnt;
                        ckmn(ans, now);
                    }
                }
                prv = x;
                x = parent[x];
            }
        } while (next_permutation(all(pos)));
        return ans;
    };
    if (1) {
        cin >> n >> t >> m;
        --t, --m;
        if (t == m) {
            exit(1);
        }
        for (int i = 1; i < n; ++i) {
            int a, b;
            cin >> a >> b;
            --a, --b;
            g[a].push_back(b);
            g[b].push_back(a);
        }
        dfs(t, t);
        memset(gg, -1, sizeof(gg));
        {
            int x = m, prv = -1;
            while (x != t) {
                for (int to: g[x]) {
                    if (to != parent[x] && to != prv) {
                        gg[to] = dp[to] + (x == m ? sum_deg[x] - depth[x] : sum_deg[x] - depth[x] - 1);
                    }
                }
                prv = x;
                x = parent[x];
            }
        }
        cout << stupid_solve();
    } else {
        n = 100;
        t = 1;
        m = 2;
        --t, --m;
        while (true) {
            if (t == m) {
                exit(1);
            }
            tops.clear();
            for (int i = 0; i < n; ++i) {
                g[i].clear();
                sum_deg[i] = 0;
                deg[i] = 0;
                dp[i] = 0;
                depth[i] = 0;
                parent[i] = 0;
            }
            for (int i = 1; i < n; ++i) {
                int a = rand(0, i - 1);
                g[a].push_back(i);
                g[i].push_back(a);
            }
            dfs(t, t);
            memset(gg, -1, sizeof(gg[0]) * n);
            {
                int x = m, prv = -1;
                while (x != t) {
                    for (int to: g[x]) {
                        if (to != parent[x] && to != prv) {
                            gg[to] = dp[to] + (x == m ? sum_deg[x] - depth[x] : sum_deg[x] - depth[x] - 1);
                        }
                    }
                    prv = x;
                    x = parent[x];
                }
            }
            int smart = not_very_smart_solve();
            int stupid = dp[m];
            if (smart != stupid) {
                cout << "NO!" << endl;
                cout << n << " " << t + 1 << " " << m + 1 << endl;
                for (int i = 1; i < n; ++i)
                    cout << parent[i] + 1 << " " << i + 1 << endl;
                trace(smart)
                trace(stupid)
                return 0;
            }
            cout << "OK!" << endl;
        }
    }
    return 0;
}

Compilation message (stderr)

mousetrap.cpp: In lambda function:
mousetrap.cpp:194:53: warning: suggest parentheses around comparison in operand of '&' [-Wparentheses]
  194 |                                 if (!used[uu] && pp != uu & to != uu && uu != parent[z])
      |                                                  ~~~^~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:66:10: warning: variable 'smart_solve' set but not used [-Wunused-but-set-variable]
   66 |     auto smart_solve = [&]() -> int {
      |          ^~~~~~~~~~~

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