Submission #418452

#	Time	Username	Problem	Language	Result	Execution time	Memory
418452		parsabahrami	Subtree (INOI20_subtree)	C++17	12 / 100	256 ms	30916 KiB

Main

// Call my Name and Save me from The Dark
#include <bits/stdc++.h>
 
using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
 
#define SZ(x)                       (int) x.size()
#define F                           first
#define S                           second

const int N = 1e5 + 10, MOD = 1e9 + 7;
int dp[N], M[N], dp2[N], up[N], low[N], H[N], rt[N], B[N], fr[N], to[N], n, m; vector<int> vec[N], adj[N];
int pd[N];

void preDFS(int v, int p = -1) {
    low[v] = H[v]; M[v] = 1;
    for (int id : adj[v]) {
        int u = fr[id] ^ to[id] ^ v;
        if (!M[u]) {
            H[u] = H[v] + 1; preDFS(u, v);
            if (low[u] > H[v]) B[id] = 1;
            low[v] = min(low[v], low[u]);
        } else if (u != p) 
            low[v] = min(low[v], H[u]);
    }
}

int Find(int v) { return !rt[v] ? v : rt[v] = Find(rt[v]); }

void Union(int u, int v) {
    u = Find(u), v = Find(v);
    if (u == v) return;
    if (SZ(vec[u]) < SZ(vec[v])) 
        swap(u, v);
    for (int w : vec[u]) 
        vec[v].push_back(w);
    rt[u] = v;
}

void DFS(int v, int p = -1) {
    vector<int> tmp;
    for (int &u : vec[v]) 
        for (int &w : adj[u])  
            if (w != p) 
                tmp.push_back(w);
            else up[v] = u;
    for (int &u : tmp) 
        DFS(u, v);
}

int calc_dp2(vector<int> &A) {
    int ret = 0, S = 0;
    for (int i = 0; i < SZ(A); i++) {
        S = A[i] * 1ll * (S + 1) % MOD;
        ret = (ret + S) % MOD;
    }
    return ret;
}

int calc_dp1(vector<int> &A) {
    int ret = calc_dp2(A), S = 1;
    fill(pd, pd + SZ(A) + 1, 0);
    for (int i = 0; i < SZ(A); i++) {
        S = 1ll * S * A[i] % MOD;
        pd[i] = S;
        if (i > 0) pd[i] = (pd[i] + pd[i - 1]) % MOD;
    }
    S = 1;
    for (int i = SZ(A) - 1; i > 1; i--) {
        S = 1ll * S * A[i] % MOD;
        ret = (ret + 1ll * S * pd[i - 2] % MOD) % MOD;
    }
    return ret;
}

void dpDFS(int v, int p = -1) {
    vector<int> A;
    if (~p) {
        int pos = find(begin(vec[v]), end(vec[v]), up[v]) - begin(vec[v]);
        swap(vec[v][pos], vec[v].back());
    }
    for (int &u : vec[v]) {
        A.push_back(1);
        for (int &w : adj[u]) 
            if (w != p) dpDFS(w, v), A.back() = A.back() * 1ll * (dp2[w] + 1) % MOD;
    }
    dp[v] = calc_dp1(A);
    if (SZ(vec[v]) > 1) {
        int S = 1;
        for (int &x : A) 
            S = 1ll * S * x % MOD;
        dp[v] = (dp[v] - S + MOD) % MOD;
    }
    if (~p) {
        A.pop_back(); 
        dp2[v] = (dp[v] - calc_dp2(A) + MOD) % MOD;
    }
}

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i++) 
        vec[i] = {i};
    for (int i = 1; i <= m; i++) {
        int u, v; scanf("%d%d", &u, &v);
        adj[fr[i] = u].push_back(i);
        adj[to[i] = v].push_back(i);
    }
    preDFS(1);
    for (int i = 1; i <= m; i++) {
        if (!B[i]) {
            int u = fr[i], v = to[i];
            Union(u, v);
        }
    }
    for (int i = 1; i <= n; i++) 
        Find(i);
    for (int i = 1; i <= n; i++) 
        if (!rt[i]) rt[i] = i;
    for (int i = 1; i <= n; i++) {
        vector<int> tm;
        for (int id : adj[i]) { 
            int u = fr[id] ^ to[id] ^ i;
            if (rt[i] != rt[u]) tm.push_back(rt[u]);
        }
        adj[i].swap(tm);
    }
    DFS(rt[1]);
    dpDFS(rt[1]);
    int ret = 0;
    for (int i = 1; i <= n; i++) 
        if (rt[i] == i) ret = (ret + dp[i]) % MOD;
    printf("%d\n", ret);
    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:103:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  103 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp:107:24: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  107 |         int u, v; scanf("%d%d", &u, &v);
      |                   ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 8
• Subtask 2: 12 / 12
• Subtask 3: 0 / 30
• Subtask 4: 0 / 50