235-Lowest Common Ancestor of a Binary Search Tree

Description

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 v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

_______6______ / \ ___2__ ___8__ / \ / \ 0 _4 7 9 / \ 3 5

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For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

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问题描述

给定二叉排序树， 找出两个节点的最小公共祖先

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问题分析

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解法1

class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { 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); else return root; } }

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解法2

class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { TreeNode tempRoot = root; while (tempRoot != null) { if(tempRoot.val < p.val && tempRoot.val < q.val) tempRoot = tempRoot.right; if(tempRoot.val > p.val && tempRoot.val > q.val) tempRoot = tempRoot.left; else return tempRoot; } return tempRoot; } }