題目

https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/

題解

哈希表解法思路來自左程云《程序員代碼面試指南》

/*** 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) {HashMap<TreeNode, TreeNode> map = new HashMap<>();preOrder(root, map);HashSet<TreeNode> set = new HashSet<>();TreeNode pNode = p;set.add(root);while (pNode != root) {set.add(pNode);pNode = map.get(pNode);}TreeNode qNode = q;while (true) {if (set.contains(qNode)) return qNode;qNode = map.get(qNode);}}public void preOrder(TreeNode node, Map<TreeNode, TreeNode> map) {if (node.left != null) {map.put(node.left, node);preOrder(node.left, map);}if (node.right != null) {map.put(node.right, node);preOrder(node.right, map);}} }

總結

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