Submission #667685

#	Time	Username	Problem	Language	Result	Execution time	Memory
667685		mychecksedad	Star Trek (CEOI20_startrek)	C++17	7 / 100	13 ms	23776 KiB

startrek

/* Author : Mychecksdead */
#include<bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef long long int ll;
typedef long double ld;
#define MOD (1000000000+7)
#define MOD1 (998244353)
#define PI 3.1415926535
#define pb push_back
#define setp() cout << setprecision(15)
#define all(x) x.begin(), x.end()
#define debug(x) cerr << #x << " is " << x << '\n';
const int N = 1e6+100, M = 1e5+10, F = 2147483646, K = 20;

ll po(ll a, ll b){
    ll res = 1;
    while(b){
        if(b&1) (res *= a) %= MOD;
        (a *= a) %= MOD;
        b >>= 1;
    }
    return res;
}

ll d, dp[N]; // subtree and parent
vector<int> g[N];
int n, X = 0, par[N], sz[N], is[N], dep[N], mx[N];

void pre(int v, int p){
    dp[v] = 0;
    par[v] = p;
    dep[v] = dep[p] + 1;
    for(int u: g[v]){
        if(u != p){
            pre(u, v);
            dp[v] |= !dp[u];
        }
    }
}
void ppre(int v, int p){
    is[v] = dp[v];
    if(p != 0){
        is[v] |= !is[p];
    }
    for(int u: g[v]){
        if(u != p){
            ppre(u, v);
        }
    }
}
void dfs(int v, int p){
    if(dep[v] % 2)
        mx[v] = max(mx[p], n - is[v]*n);
    else
        mx[v] = max(mx[p], is[v]*n);
    for(int u: g[v]){
        if(u != p){
            dfs(u, v);
        }
    }
}

void solve(){
    cin >> n >> d;
    for(int i = 0 ; i < n - 1; ++i){
        int u, v; cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }
    if(n == 2){
        cout << po(4, d); return;
    }
    par[0] = 0;
    dp[0] = is[0] = 0;
    dep[0] = -1;
    pre(1, 0);
    ppre(1, 0);
    dfs(1, 0);

    for(int i = 1; i <= n; ++i) X += 1 - is[i];

    // dfs(1, 0);

    ll ans = max(X, mx[1]);

    for(int i = 2; i <= n; ++i){
        int m = mx[i], v = i;

        if(!(dep[i] % 2 && is[i]))
            if(is[i])
                m = max(X, m);
            else{
                m = max(n - X, m);
            }
        // cout << m << ' ';
        (ans += m) %= MOD; 
    }

    cout << ans;
}




int main(){
    cin.tie(0); ios::sync_with_stdio(0);
    int T = 1, aa;
    // cin >> T;aa=T;
    while(T--){
        // cout << "Case #" << aa-T << ": ";
        solve();
        cout << '\n';
    }
    return 0;
 
}

Compilation message (stderr)

startrek.cpp: In function 'void solve()':
startrek.cpp:91:11: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   91 |         if(!(dep[i] % 2 && is[i]))
      |           ^
startrek.cpp:89:24: warning: unused variable 'v' [-Wunused-variable]
   89 |         int m = mx[i], v = i;
      |                        ^
startrek.cpp: In function 'int main()':
startrek.cpp:109:16: warning: unused variable 'aa' [-Wunused-variable]
  109 |     int T = 1, aa;
      |                ^~

• 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