Submission #1379625

---

Source Code Expand

/*
 _    _    _______   _    _
| |  / /  |  _____| | |  / /
| | / /   | |       | | / /
| |/ /    | |_____  | |/ /
| |\ \    |  _____| | |\ \
| | \ \   | |       | | \ \
| |  \ \  | |_____  | |  \ \
|_|   \_\ |_______| |_|   \_\

*/
/*#include <iostream>
#include <cstdio>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <vector>
#include <cstring>
#include <string>
#include <iomanip>
#include <cmath>
#include <algorithm>
#include <assert.h>*/

#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef double ld;
typedef pair <int, int> PII;
typedef pair <ll, ll> PLL;

#define F first
#define S second
#define pb push_back
#define eb emplace_back
#define right(x) x << 1 | 1
#define left(x) x << 1
#define forn(x, a, b) for (int x = a; x <= b; ++x)
#define for1(x, a, b) for (int x = a; x >= b; --x)
#define mkp make_pair
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define y1 kekekek

const ll ool = 1e18 + 9;
const int oo = 1e9 + 9, base = 1e9 + 7;
const ld eps = 1e-7;
const int N = 2e6 + 6;

int n;
ll d[N], a[N];
vector < int > g[N];

void dfs(int v, int par) {
    if (sz(g[v]) == 1) {
        d[v] = a[v];
        return;
    }
    ll sum = 0, mx = 0;
    for (auto to : g[v]) {
        if (to == par) continue;
        dfs(to, v);
        sum += d[to];
        mx = max(mx, d[to]);
    }
    ll need = sum - a[v];
    ll lim = (mx <= sum / 2 ? sum / 2 : sum - mx);
    if (lim < need || a[v] > sum) {
        cout << "NO\n";
        exit(0);
    }
    d[v] = a[v] - need;
    if (d[v] < 0) {
        cout << "NO\n";
        exit(0);
    }
}

int main() {
	ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);

	cin >> n;
	forn(i, 1, n) {
        cin >> a[i];
	}

	forn(i, 1, n - 1) {
        int x, y;
        cin >> x >> y;
        g[x].eb(y);
        g[y].eb(x);
	}
	
	if (n == 2) {
        cout << (a[1] == a[2] ? "YES" : "NO") << "\n";
        return 0;
	}

    int root = 1;
    while (sz(g[root]) == 1) ++root;

    dfs(root, 0);

    cout << (d[root] == 0 ? "YES" : "NO") << "\n";

	return 0;
}

Submission Info

Judge Result