Submission #286870

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Source Code Expand

#!/usr/bin/env python


def read():
    n, x = map(int, raw_input().split())
    x -= 1

    isExist = map(int, raw_input().split())
    isExist[x] = 1
    
    adj = [[] for i in range(n)]
    
    for i in range(n - 1):
        s, t = map(int, raw_input().split())
        s -= 1
        t -= 1
        adj[s].append(t)
        adj[t].append(s)
    
    
    return x, isExist, adj


def dfs(curr, pre, isExist, adj):
    
    ret = 0
    
    for nex in adj[curr]:
        if nex == pre:
            continue

        t = dfs(nex, curr, isExist, adj)

        if t != -1:
            ret += t + 2

    return -1 if ret == 0 and not isExist[curr] else ret


def work((x, isExist, adj)):
    print dfs(x, -1, isExist, adj)


if __name__ == "__main__":
    work(read())

Submission Info

Judge Result