81N4RY TR33

import numpy as np
class Solution:
    def __init__(self):
        self.visited = [] # label visited nodes (and if nodes are visited again then graph is cyclic)

    def validateBinaryTreeNodes(self, n: int, leftChild: List[int], rightChild: List[int]) -> bool:
        self.visited = np.array([0]*n)
        isTree = self.visitNode(leftChild, rightChild, 0)
        if (isTree == False) or len(set(self.visited)) > 1: # if cyclic then isTree is false; if visited has 0s and 1s then not all nodes visited (thus there may be more than one tree)
            return False
        return True

    def visitNode(self, leftChild, rightChild, node):
        if self.visited[node] == 0:
            self.visited[node] = 1
        else:
            return False # node has been visited already (graph is cyclic and thus not a tree)
        isTree = True
        if leftChild[node] != -1: # check if there is left child
            isTree = self.visitNode(leftChild, rightChild, leftChild[node]) # now visit left child node (recursive)
        if rightChild[node] != -1: # check if there is right child
            isTree = isTree and self.visitNode(leftChild, rightChild, rightChild[node]) # now visit right child node (recursive)
        return isTree