Submission #1381007

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Source Code Expand

#include <bits/stdc++.h>
 
#define pii pair<int, int>
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define ll long long 
#define ull unsigned long long 
#define ld long double
#define sz(v) int(v.size())
#define all(v) v.begin(), v.end()
 
#define y1 what
 
using namespace std;
 
const int N = (int) 1e6 + 10;
const int M = (int) 101;
const ll big =  (1LL << 51);
const ll LINF = (ll) 1e18;
const int INF = (int) 1e9 + 7;
const int INF1 = (int) 1e9 + 3;
const double EPS = (double) 1e-6;
const double PI =  3.14159265359;
 
int n;
int root;
ll a[N];
vector<int> v[N];
 
ll calc(int x, int p = -1) {
  ll mx = 0, leaf = 1;
  ll sum = 0;
  for (auto it : v[x]) {
    if (it == p)
      continue;
    ll rem = calc(it, x);
    sum += rem;
    mx = max(mx, rem);
    leaf = 0;
  }
  if (leaf) 
    return a[x];
  ll z = sum - a[x];
  if (z < 0) {
    cout << "NO";
    return 0;
  }
  ll max_matching;
  if (mx > sum / 2) {
    max_matching = sum - mx;
  } else {
    max_matching = sum / 2;
  }
  if (max_matching >= z) {
    return a[x] - z;
  } else {
    cout << "NO";
    exit(0);
  }
}
 
int main() {
    #define fn "balls"
    #ifdef witch
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #else
//        freopen(fn".in", "r", stdin);
//        freopen(fn".out", "w", stdout);
    #endif
    srand(time(0));
    cin >> n;
    for (int i = 1; i <= n; i++) {
      cin >> a[i];
    }
    for (int i = 1, x, y; i < n; i++) {
      cin >> x >> y;
      v[x].pb(y);
      v[y].pb(x);
    }
    root = 1;
    for (int i = 1; i <= n; i++) {
      if (sz(v[i]) > 1) {
        root = i;
      }
    }
    if (n == 2) {
      if (a[1] == a[2]) 
        cout << "YES";
      else 
        cout << "NO";
      return 0;
    }
    cout << (calc(root) == 0 ? "YES" : "NO");
    return 0;
}

Submission Info

Judge Result