DFS_298_二叉樹最長連續序列

題目描述

思路

• dfs，若在遞歸過程中 不滿足要求，長度重新置爲1

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def longestConsecutive(self, root: TreeNode) -> int:
        if not root: return 0
        self.ans = 0

        def dfs(node, parent, parent_path):
            if not node: return
            cur = 1  # 如果下面不成立，cur爲1
            if node.val == parent:
                cur += parent_path

            self.ans = max(self.ans, cur)
            dfs(node.left, node.val+1, cur)
            dfs(node.right, node.val+1, cur)

        dfs(root, root.val+1, 1)  # 由於root沒有父節點, 這裏第3個參數值可隨意設置
        return self.ans