MediumNo. 0549LeetCode Premium
Binary Tree Longest Consecutive Sequence II — LeetCode 549 Python Solution
- Pattern
- Tree Traversal
- Topics
- Tree, Depth-First Search, Binary Tree
- Reading time
- 5 min
- Source
- leetcode.com
The problem
Given the root of a binary tree, return the length of the longest consecutive path in the tree. A consecutive path is a path where the values of the consecutive nodes in the path differ by one.
Example
- Input
- root = [1,2,3]
- Output
- 2
- Explanation
- The longest consecutive path is [1, 2] or [2, 1].
Python solution
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def longestConsecutive(self, root: TreeNode) -> int:
def dfs(root):
if root is None:
return [0, 0]
nonlocal ans
incr = decr = 1
i1, d1 = dfs(root.left)
i2, d2 = dfs(root.right)
if root.left:
if root.left.val + 1 == root.val:
incr = i1 + 1
if root.left.val - 1 == root.val:
decr = d1 + 1
if root.right:
if root.right.val + 1 == root.val:
incr = max(incr, i2 + 1)
if root.right.val - 1 == root.val:
decr = max(decr, d2 + 1)
ans = max(ans, incr + decr - 1)
return [incr, decr]
ans = 0
dfs(root)
return ansComplexity
- Time
- O(V+E)
- Space · auxiliary
- O(V)
Pattern: Tree Traversal
Choose the order — preorder, inorder, postorder, level — and the problem solves itself. LeetCode 549. Binary Tree Longest Consecutive Sequence II is filed here because LeetCode tags it Tree and Binary Tree, which is the vocabulary this hub collects.
The tree traversal guide has the Python template for the pattern and the 225 LeetCode problems that use it.
Related problems
| No. | Problem | Difficulty |
|---|---|---|
| 0543 | Diameter of Binary Tree | Easy |
| 0098 | Validate Binary Search Tree | Medium |
| 0099 | Recover Binary Search Tree | Medium |
| 0100 | Same Tree | Easy |
| 0101 | Symmetric Tree | Easy |
| 0104 | Maximum Depth of Binary Tree | Easy |
Frequently asked questions
- How hard is LeetCode 549. Binary Tree Longest Consecutive Sequence II?
LeetCode 549. Binary Tree Longest Consecutive Sequence II is rated Medium on LeetCode.
- What is the time complexity of LeetCode 549. Binary Tree Longest Consecutive Sequence II?
The Python solution on this page runs in O(V+E).
- What is the space complexity of LeetCode 549. Binary Tree Longest Consecutive Sequence II?
The Python solution on this page uses O(V) auxiliary space.
- What topics does LeetCode 549. Binary Tree Longest Consecutive Sequence II cover?
LeetCode 549. Binary Tree Longest Consecutive Sequence II is tagged Tree, Depth-First Search and Binary Tree on LeetCode.
- Is LeetCode 549. Binary Tree Longest Consecutive Sequence II a premium problem?
Yes. LeetCode 549. Binary Tree Longest Consecutive Sequence II is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.