Submission #3948359

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Source Code Expand

#include<iostream>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<map>
#include<set>
#include<algorithm>
#include<functional>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cassert>
#include<ctime>
using namespace std;

#define mind(a,b) (a>b?b:a)
#define maxd(a,b) (a>b?a:b)
#define absd(x) (x<0?-(x):x)
#define pow2(x) ((x)*(x))
#define rep(i,n) for(int i=0; i<n; ++i)
#define repr(i,n) for(int i=n-1; i>=0; --i)
#define repl(i,s,n) for(int i=s; i<=n; ++i)
#define replr(i,s,n) for(int i=n; i>=s; --i)
#define repf(i,s,n,j) for(int i=s; i<=n; i+=j)
#define repe(e,obj) for(auto e : obj)

#define SP << " " <<
#define COL << " : " <<
#define COM << ", " <<
#define ARR << " -> " <<
#define PNT(STR) cout << STR << endl
#define POS(X,Y) "(" << X << ", " << Y << ")"
#define DEB(A) " (" << #A << ") " << A
#define DEBREP(i,n,val) for(int i=0; i<n; ++i) cout << val << " "; cout << endl
#define ALL(V) (V).begin(), (V).end()
#define INF 1000000007
#define INFLL 1000000000000000007LL
#define EPS 1e-9

typedef unsigned int uint;
typedef unsigned long ulong;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
#define P_TYPE int
typedef pair<P_TYPE, P_TYPE> P;
typedef pair<P, P_TYPE> PI;
typedef pair<P_TYPE, P> IP;
typedef pair<P, P> PP;
typedef priority_queue<P, vector<P>, greater<P> > pvqueue;

#define N 100007
#define MOD 1000000007

int n;
vector<int> g[N];

ll memo[N][2];
ll dfs(int v, int s, int p = -1) {
  if(memo[v][s] != -1) {
    return memo[v][s];
  }
  if((p != -1 && g[v].size() == 1) || (p == -1 && g[v].size() == 0)) {
    return s == 0 ? 2 : 1;
  }
  ll r0 = 1, r1 = 1;
  repe(w, g[v]) {
    if(w == p) continue;
    if(s == 0) r0 = (r0 * dfs(w, 1, v)) % MOD;
    r1 = (r1 * dfs(w, 0, v)) % MOD;
  }
  return memo[v][s] = (s == 0 ? r0 + r1 : r1) % MOD;
}

int main() {
  cin >> n;
  rep(i, n-1) {
    int x, y; cin >> x >> y; --x; --y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  rep(i, n) rep(j, 2) memo[i][j] = -1;
  cout << dfs(0, 0) << endl;
  return 0;
}

Submission Info

Judge Result