LeetCode: Lowest Common Ancestor of a Binary Search Tree二叉搜索树最近公共祖先 不念不忘少年蓝@ 2021-06-24 16:10 273阅读 0赞 **试题:** Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Given binary search tree: root = \[6,2,8,0,4,7,9,null,null,3,5\] Example 1: Input: root = \[6,2,8,0,4,7,9,null,null,3,5\], p = 2, q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = \[6,2,8,0,4,7,9,null,null,3,5\], p = 2, q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition. **代码:** 如果存在公共祖先,那么这个祖先必然大于左边,小于右边。三种情况互相对立,直接返回结果就行。 /** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if(root==null) return null; if(root.val>p.val && root.val>q.val){ return lowestCommonAncestor(root.left, p, q); }else if(root.val<p.val && root.val<q.val){ return lowestCommonAncestor(root.right, p, q); }{ return root; } } }
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