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77 lines
1.8 KiB
Python
77 lines
1.8 KiB
Python
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"""
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236. Lowest Common Ancestor of a Binary Tree
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Difficulty: Medium
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https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/
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──────────────────────────────────────────────────
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Given a binary tree, find the lowest common ancestor (LCA) of two
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given nodes in the tree.
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According to the definition of LCA on Wikipedia: “The lowest
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common ancestor is defined between two nodes p and q as the lowest
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node in T that has both p and q as descendants (where we allow a node
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to be a descendant of itself).”
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Example 1:
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Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
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Output: 3
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Explanation: The LCA of nodes 5 and 1 is 3.
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Example 2:
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Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
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Output: 5
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Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a
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descendant of itself according to the LCA definition.
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Example 3:
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Input: root = [1,2], p = 1, q = 2
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Output: 1
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Constraints:
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• The number of nodes in the tree is in the range [2, 10^5].
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• -10^9 <= Node.val <= 10^9
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• All Node.val are unique.
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• p != q
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• p and q will exist in the tree.
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"""
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, x):
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# self.val = x
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# self.left = None
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# self.right = None
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class Solution:
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def lowestCommonAncestor(
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self, root: "TreeNode", p: "TreeNode", q: "TreeNode"
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) -> "TreeNode":
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if not root:
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return None
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if root == p or root == q:
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return root
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l = self.lowestCommonAncestor(root.left, p, q)
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r = self.lowestCommonAncestor(root.right, p, q)
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if l and r:
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return root
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else:
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return l or r
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