Submission #576251

#	Time	Username	Problem	Language	Result	Execution time	Memory
576251		piOOE	Star Trek (CEOI20_startrek)	C++17	7 / 100	2 ms	2644 KiB

startrek

#include <bits/stdc++.h>

using namespace std;

//#include <ext/pb_ds/assoc_container.hpp>
//
//using namespace __gnu_pbds;
//
//template <typename T>
//using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;


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

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

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

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; }

const int N = 100001, mod = 1e9 + 7;

int mul(int a, int b) {
    return a * (ll)b % mod;
}

int add(int a, int b) {
    return a + b >= mod ? a + b - mod : a + b;
}

int fastp(int a, ll p) {
    int ans = 1;
    for (; p > 0; a = mul(a, a), p >>= 1) {
        if (p & 1) {
            ans = mul(ans, a);
        }
    }
    return ans;
}

int inv(int a) {
    return fastp(a, mod - 2);
}

vector<int> g[N];
int cntLoosing[N], dpWin[N], dpLose[N], grandpa[N];

bool dp[N], dp2[N];

int chosen = -1;

void dfs(int v, int p, int pp) {
    dp[v] = false;
    grandpa[v] = pp;
    bool oh = false;
    for (int to : g[v]) {
        if (to != p) {
            oh = true;
            dfs(to, v, (pp == -1 ? to : pp));
            if (!dp[to]) {
                dpWin[v] = add(dpWin[v], dpLose[to]);
                dp[v] = true;
            } else {
                dpLose[v] = add(dpLose[v], dpWin[to]);
            }
        }
    }
    if (!oh)
        dpLose[v] = 1;
}

void gfs(int v, int p) {
    for (int to : g[v]) {
        if (to != p) {
            cntLoosing[v] += !dp[to];
        } else if (!dp[p] || cntLoosing[p] == 1 && !dp[v]){
            cntLoosing[v] += 1;
        }
    }
    dp[v] = cntLoosing[v];
    for (int to : g[v]) {
        if (to != p) {
            gfs(to, v);
        }
    }
}

void dfs2(int v, int p) {
    dp2[v] = false;
    for (int to : g[v]) {
        if (to != p) {
            dfs2(to, v);
            if (!dp2[to]) {
                dp2[v] = true;
            }
        }
    }
}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    ll d;
    cin >> n >> d;
    if (n == 2) {
        cout << fastp(4, d);
        return 0;
    }
    for (int i = 0; i < n - 1; ++i) {
        int a, b;
        cin >> a >> b;
        --a, --b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    if (d == 1) {
        int cntWin = 0;
        dfs(0, -1, -1);
        gfs(0, -1);
        cntWin = count(dp, dp + n, true);
        int ans = (dp[0] * mul(cntWin, n));
        dfs2(0, -1);
        for (int v = 0; v < n; ++v) {
            if (dp2[v]) {
                ans = add(ans, (n - cntWin) * dp2[0]);
            } else {
                if (dp2[0]) {
                    if (dpWin[0] != dpLose[v]) {
                        ans = add(ans, n - cntWin);
                    }
                } else {
                    if (v == 0) {
                        ans = add(ans, n - cntWin);
                    }
                    else if (grandpa[v] != v && dpWin[grandpa[v]] == dpLose[v]) {
                        ans = add(ans, n - cntWin);
                    }
                }
            }
        }
        cout << ans;
    }
    return 0;
}

Compilation message (stderr)

startrek.cpp: In function 'void gfs(int, int)':
startrek.cpp:97:49: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   97 |         } else if (!dp[p] || cntLoosing[p] == 1 && !dp[v]){
      |                              ~~~~~~~~~~~~~~~~~~~^~~~~~~~~

• Subtask 1: 0 / 0
• Subtask 2: 7 / 7
• Subtask 3: 0 / 8
• Subtask 4: 0 / 15
• Subtask 5: 0 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15