コード#コード#

n = int(input())

li = list(map(int, input().split()))
r = int(input())

tree = [[]for _ in range(n)]
root = 0
ans = 0

for idx, i in enumerate(li):
    if i == -1:
        root = idx
        continue
    if idx == r:
        continue
    tree[i].append(idx)


def dfs(v):
    global ans
    if len(tree[v]) ==0:
        ans += 1
        return
    for i in tree[v]:
        dfs(i)

if root != r:
    dfs(root)
print(ans)

方法

持ち物