Submission #947077

#TimeUsernameProblemLanguageResultExecution timeMemory
947077GrindMachineStar Trek (CEOI20_startrek)C++17
43 / 100
1073 ms24456 KiB
#include <bits/stdc++.h> #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> using namespace std; using namespace __gnu_pbds; template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; typedef long long int ll; typedef long double ld; typedef pair<int,int> pii; typedef pair<ll,ll> pll; #define fastio ios_base::sync_with_stdio(false); cin.tie(NULL) #define pb push_back #define endl '\n' #define sz(a) (int)a.size() #define setbits(x) __builtin_popcountll(x) #define ff first #define ss second #define conts continue #define ceil2(x,y) ((x+y-1)/(y)) #define all(a) a.begin(), a.end() #define rall(a) a.rbegin(), a.rend() #define yes cout << "Yes" << endl #define no cout << "No" << endl #define rep(i,n) for(int i = 0; i < n; ++i) #define rep1(i,n) for(int i = 1; i <= n; ++i) #define rev(i,s,e) for(int i = s; i >= e; --i) #define trav(i,a) for(auto &i : a) template<typename T> void amin(T &a, T b) { a = min(a,b); } template<typename T> void amax(T &a, T b) { a = max(a,b); } #ifdef LOCAL #include "debug.h" #else #define debug(x) 42 #endif /* refs: edi https://youtu.be/Tjv78ZThV5c */ const int MOD = 1e9 + 7; const int N = 1e5 + 5; const int inf1 = int(1e9) + 5; const ll inf2 = ll(1e18) + 5; vector<ll> adj[N]; vector<ll> dp1(N), dp2(N), dp3(N); void dfs1(ll u, ll p){ dp1[u] = 0; trav(v,adj[u]){ if(v == p) conts; dfs1(v,u); dp1[u] += (dp1[v] == 0); } } void dfs2(ll u, ll p){ trav(v,adj[u]){ if(v == p) conts; ll val = dp2[u]-(dp1[v] == 0); dp2[v] += (val == 0); dfs2(v,u); } } void dfs3(ll u, ll p, ll depth, ll r){ if(!dp1[u]){ ll val = 1; if(depth&1) val = 0; dp3[r] -= dp2[r]; dp3[r] += val; } vector<ll> win,lose; trav(v,adj[u]){ if(v == p) conts; if(dp1[v]) win.pb(v); else lose.pb(v); } if(sz(lose) == 0){ trav(v,win){ dfs3(v,u,depth+1,r); } } else if(sz(lose) == 1){ dfs3(lose[0],u,depth+1,r); } } void solve(int test_case) { ll n,d; cin >> n >> d; rep1(i,n-1){ ll u,v; cin >> u >> v; adj[u].pb(v), adj[v].pb(u); } dfs1(1,-1); rep1(i,n) dp2[i] = dp1[i]; dfs2(1,-1); rep1(i,n){ amin(dp1[i],1ll); amin(dp2[i],1ll); } rep1(r,n){ dfs1(r,-1); dp3[r] = dp2[r]*n; dfs3(r,-1,0,r); } ll win_ways_w = 0, lose_ways_w = 0; rep1(r,n){ if(dp2[r]){ win_ways_w += n; } else{ lose_ways_w += n; } } ll win_ways_l = 0, lose_ways_l = 0; rep1(r,n){ win_ways_l += dp3[r]; lose_ways_l += n-dp3[r]; } ll win = 0, lose = 0; rep1(i,n){ if(dp2[i]) win++; else lose++; } rev(i,d-1,1){ ll win2 = (win*win_ways_w + lose*win_ways_l)%MOD; ll lose2 = (win*lose_ways_w + lose*lose_ways_l)%MOD; win = win2, lose = lose2; } ll ans = 0; if(dp2[1]){ ans += n*win; } ans += dp3[1]*lose; ans %= MOD; cout << ans << endl; } int main() { fastio; int t = 1; // cin >> t; rep1(i, t) { solve(i); } return 0; }
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