Submission #1227657

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define REP(i,n) for(int i=0;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)
#define INF 1<<29
#define LINF LLONG_MAX/3
#define MP make_pair
#define PB push_back
#define pb push_back
#define EB emplace_back
#define ALL(v) (v).begin(),(v).end()
#define all(v) ALL(v)
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
constexpr double eps = 1e-14; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

constexpr ll MN = 100011;
ll N;

array<ll,MN> A;
array<vector<ll>,MN> g;
bool ans=true;

ll dfs(ll c,ll p){
    // leaf
    if(sz(g[c])==1) return A[c];
    // not leaf
    vector<ll> ch;
    for(auto v:g[c]) if(v!=p){
        ch.pb(dfs(v,c));
    }
    ll mx = *max_element(all(ch));
    ll sum = accumulate(all(ch),0);

    ll np = 2*A[c]-sum;  // connect for the direction of parent
    ll cp = (sum-np)/2;

    if(np<0 or (sum-np)%2==1){ ans=false; }
    if(sum-mx<cp){ ans=false; }
    cout << "dfs(" << c << "," << p << ") = " << np << endl;
    return np;
}

int main(){
    cin >> N;
    rep(i,N) cin>>A[i];
    rep(i,N-1){
        ll a,b;cin>>a>>b;a--;b--;
        g[a].pb(b);
        g[b].pb(a);
    }

    if(N==2){
        cout << (A[0]==A[1] ? "YES" : "NO") << endl;
        return 0;
    }

    ll tmp;
    for(int i=0;i<N;i++) if(sz(g[i])>1){
        cout << "root:" << i << endl;
        tmp = dfs(i,-1);
        break;
    }
    if(!ans){
        cout << "NO" << endl;
        return 0;
    }
    if(tmp==0) cout << "YES" << endl;
    else cout << "NO" << endl;
}

Submission Info

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