Problem p03809 (python)

Fixed submission:
import sys

sys.setrecursionlimit(10 ** 6)


def dfs(v, p, aaa):
    if len(links[v]) == 1:
        return aaa[v]

    children = []
    for u in links[v]:
        if u == p:
            continue
        result = dfs(u, v, aaa)
        if result == -1:
            return -1
        children.append(result)

    if len(children) == 1:
        if aaa[v] != children[0]:
            return -1
        return children[0]

    c_sum = sum(children)
    c_max = max(children)
    o_max = c_sum - c_max

    if o_max >= c_max:
        max_pairs = c_sum // 2
    else:
        max_pairs = o_max
    min_remain = c_sum - max_pairs
    if not min_remain <= aaa[v] <= c_sum:
        return -1

    return aaa[v] * 2 - c_sum


def solve(n, aaa, links):
    if n == 2:
        return aaa[0] == aaa[1]
    # 葉でない頂点探し
    s = 0
    while len(links[s]) == 1:
        s += 1
    return dfs(s, -1, aaa) == 0


n = int(input())
aaa = list(map(int, input().split()))
links = [set() for _ in range(n)]
for line in sys.stdin:
    a, b = map(int, line.split())
    a -= 1
    b -= 1
    links[a].add(b)
    links[b].add(a)

print('YES' if solve(n, aaa, links) else 'NO')

Buggy submission (verdict: Runtime Error):
import sys

sys.setrecursionlimit(10 ** 6)


def dfs(v, p, aaa):
    if len(links[v]) == 1:
        return aaa[v]

    children = []
    for u in links[v]:
        if u == p:
            continue
        result = dfs(u, v, aaa)
        if result == -1:
            return -1
        children.append(result)

    if len(children) == 1:
        if aaa[v] != children[0]:
            return -1
        return children[0]

    c_sum = sum(children)
    c_max = max(children)
    o_max = c_sum - c_max

    if o_max >= c_max:
        max_pairs = c_sum // 2
    else:
        max_pairs = o_max
    min_remain = c_sum - max_pairs
    if not min_remain <= aaa[v] <= c_sum:
        return -1

    return aaa[v] * 2 - c_sum


def solve(n, aaa, links):
    # 葉でない頂点探し
    s = 0
    while len(links[s]) == 1:
        s += 1

    return dfs(s, -1, aaa) == 0


n = int(input())
aaa = list(map(int, input().split()))
links = [set() for _ in range(n)]
for line in sys.stdin:
    a, b = map(int, line.split())
    a -= 1
    b -= 1
    links[a].add(b)
    links[b].add(a)

print('YES' if solve(n, aaa, links) else 'NO')

Buggy submission (verdict: Runtime Error):
import sys

sys.setrecursionlimit(10 ** 5 + 5)


def dfs(v, p, aaa):
    if len(links[v]) == 1:
        return aaa[v]

    children = []
    for u in links[v]:
        if u == p:
            continue
        result = dfs(u, v, aaa)
        if result == -1:
            return -1
        children.append(result)

    if len(children) == 1:
        if aaa[v] != children[0]:
            return -1
        return children[0]

    c_sum = sum(children)
    c_max = max(children)
    o_max = c_sum - c_max

    if o_max >= c_max:
        max_pairs = c_sum // 2
    else:
        max_pairs = o_max
    min_remain = c_sum - max_pairs
    if not min_remain <= aaa[v] <= c_sum:
        return -1

    return aaa[v] * 2 - c_sum


def solve(n, aaa, links):
    # 葉でない頂点探し
    s = 0
    while len(links[s]) == 1:
        s += 1

    return dfs(s, -1, aaa) == 0


n = int(input())
aaa = list(map(int, input().split()))
links = [set() for _ in range(n)]
for line in sys.stdin:
    a, b = map(int, line.split())
    a -= 1
    b -= 1
    links[a].add(b)
    links[b].add(a)

print('YES' if solve(n, aaa, links) else 'NO')