235. 二叉搜索树的最近公共祖先

递归

/**
 * 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) {
        //二叉搜索树的特点，有序， 先序递归
        if(root == null ) return null;
        //中 不处理
        if(root.val > p.val && root.val > q.val ) {
            TreeNode left = lowestCommonAncestor(root.left, p, q );
            return left;
        }
        if(root.val < p.val && root.val < q.val ) {
            TreeNode right = lowestCommonAncestor(root.right, p, q );
            return right;
        }
        return root;
    }
}

迭代

/**
 * 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) {
        while(root != null ) {
            if(root.val > p.val && root.val > q.val ) {
                root = root.left;
            } else if(root.val < p.val && root.val < q.val ) {
                root = root.right;
            } else {
                return root;
            }
        }
        return root;
    }
}