Binary Tree Longest Consecutive Sequence
简单题，只要单向递增的
错误点：
- +1，不是>=
- 注意是top.left, top.right, 不是root.left, root.right：debug log：打印每层root.val和当前curlen
https://repl.it/Ccr6/3 (iteration: pre-order traversal)
https://repl.it/Ccr6/4 (recursion)
# Given a binary tree, find the length of the longest consecutive sequence path.
# The path refers to any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The longest consecutive path need to be from parent to child (cannot be the reverse).
# For example,
# 1
#
# 3
# /
# 2 4
#
# 5
# Longest consecutive sequence path is 3-4-5, so return 3.
# 2
#
# 3
# /
# 2
# /
# 1
# Longest consecutive sequence path is 2-3,not3-2-1, so return 2.
from collections import deque
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def longestConsecutive(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if not root: return 0
stk = deque([(root,1)])
maxLen = 0
while stk:
top, curlen = stk.pop()
maxLen = max(curlen, maxLen)
if top.left:
stk.append((top.left, curlen+1 if top.left.val==top.val+1 else 1)) # error: root.left
if top.right:
stk.append((top.right, curlen+1 if top.right.val==top.val+1 else 1))
return maxLen
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def longestConsecutive(self, root):
"""
:type root: TreeNode
:rtype: int
"""
def dfs(root, pre, curLen):
if root.val==pre+1: # +1, not >=
curLen+=1
else:
curLen=1
self.maxLen=max(self.maxLen, curLen)
if root.left:
dfs(root.left, root.val, curLen)
if root.right:
dfs(root.right, root.val, curLen)
self.maxLen = 0
if not root: return 0
dfs(root, float('-inf'), 0)
return self.maxLen