Binary Tree Longest Consecutive Sequence

题目描述

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,not 3-2-1, so return 2.

解题方法

• recursion,在参数中包含当前的连续seq长度
• 如果left, right child的value是连续的，那么就将长度+1传入下一个call

Solution

class Solution(object):
    def longestConsecutive(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0

        self.result = 0
        self.helper(root, 1)

        return self.result

    def helper(self, root, curLen):
        self.result = curLen if curLen > self.result else self.result
        if root.left:
            if root.left.val == root.val + 1:
                self.helper(root.left, curLen + 1)
            else:
                self.helper(root.left, 1)
        if root.right:
            if root.right.val == root.val + 1:
                self.helper(root.right, curLen + 1)
            else:
                self.helper(root.right, 1)

Reference