Submission #635621

#TimeUsernameProblemLanguageResultExecution timeMemory
635621406Subtree (INOI20_subtree)C++17
12 / 100
71 ms34728 KiB
#include <bits/stdc++.h> using ll = long long; using namespace std; #define forn(a, b) for (int a = 0; a < (b); a++) #define rofn(a, b) for (int a = (b) - 1; a >= 0; a--) #define LOG(a) (31 - __builtin_clz(a)) #define chmx(a, b) a = max(a, b) #define chmn(a, b) a = min(a, b) #define pb push_back #define gc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++) char buf[1<<21],*p1,*p2; inline int read() { int x = 0, f = 1; char c; while(!isdigit(c = gc())) if(c=='-') f=-1; while(isdigit(c)) x = (x<<3)+(x<<1)+(c^48), c = gc(); return x * f; } const ll INFL = 1ll << 60; const int INF = 1 << 29; const int N = 1e5 + 50; const int MOD = 1e9 + 7; ll pw(ll a, ll b) { a %= MOD; b %= (MOD - 1); ll re = 1; while (b) { if (b & 1) re = (re * a) % MOD; a = (a * a) % MOD; b >>= 1; } return re; } ll dp[N]; int h[N], par[N], n, m; bitset<N> mark; vector<int> adj[N]; void dfs(int v) { mark[v] = true; dp[v] = 1; vector<int> unp; for (auto u: adj[v]) { if (!mark[u]) { par[u] = v; h[u] = h[v] + 1; dfs(u); dp[v] = (dp[v] * (dp[u] + 1)) % MOD; } else if (u != par[v] && h[u] > h[v]) { unp.pb(u); } } for (auto u: unp) { vector<ll> X; int last = n; while (u != par[v]) { X.pb((dp[u] * pw((dp[last] + 1), MOD - 2)) % MOD); if (X.back() < 0) X.back() += MOD; last = u; u = par[u]; } dp[v] = 0; reverse(X.begin(), X.end()); vector<ll> pref, P, suf; suf.pb(1); for (int i = X.size(); i >= 2; i--) { suf.pb((suf.back() * X[i - 1]) % MOD); } reverse(suf.begin(), suf.end()); pref.pb(X[0]); for (int i = 1; i < X.size(); i++) pref.pb((pref.back() * X[i]) % MOD); P.resize(pref.size()); partial_sum(pref.begin(), pref.end(), P.begin()); for (int i = 2; i < X.size(); i++) { dp[v] += (suf[i] * P[i - 2]) % MOD; if (dp[v] >= MOD) dp[v] -= MOD; } ll kol = suf.front(); for (int i = 1; i < X.size(); i++) { dp[v] += (kol * pw(X[i], MOD - 2)) % MOD; if (dp[v] >= MOD) dp[v] -= MOD; } } } signed main() { ios::sync_with_stdio(0), cin.tie(0); cin >> n >> m; for (int i = 0; i < m; i++) { int u, v; cin >> u >> v; u--, v--; adj[v].pb(u); adj[u].pb(v); } par[0] = -1; dfs(0); ll ans = 0; for (int i = 0; i < n; i++) { ans += dp[i]; if (ans >= MOD) ans -= MOD; } cout << ans << '\n'; return 0; }

Compilation message (stderr)

Main.cpp: In function 'void dfs(int)':
Main.cpp:83:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |         for (int i = 1; i < X.size(); i++)
      |                         ~~^~~~~~~~~~
Main.cpp:89:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   89 |         for (int i = 2; i < X.size(); i++) {
      |                         ~~^~~~~~~~~~
Main.cpp:96:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   96 |         for (int i = 1; i < X.size(); i++) {
      |                         ~~^~~~~~~~~~
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