235. 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.

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    private boolean find (TreeNode root,TreeNode p){        if(root == p)return true;        if(root == null)return false;        return (find(root.left,p)||find(root.right,p));    }    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {             if(root==p||root==q)return root;                if(find(root.left,p)&&find(root.left,q))return lowestCommonAncestor(root.left,p,q);        if(find(root.right,p)&&find(root.right,q))return lowestCommonAncestor(root.right,p,q);          return root;    }}