leetcode:Lowest Common Ancestor of a Binary Search Tree

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

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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题目分析：求给定二叉排序树的最近公共祖先

1.当一个节点的值大于等于根节点，另一个节点的值小于等于根节点，则返回根节点

2. 当两个节点的值都小于根节点，在根节点的左边遍历搜索

3. 当两个节点的值都大于根节点，在根节点的右边遍历搜索

代码如下：

public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        if((p.val<=root.val&&q.val>=root.val)||(p.val>=root.val&&q.val<=root.val))        return root;        else if(p.val<root.val&&q.val<root.val)        {        return lowestCommonAncestor(root.left,p,q);        }        else         {        return lowestCommonAncestor(root.right,p,q);        }    }