题目

解题代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode searchBST(TreeNode root, int val) {
        if(root == null) return null;
        if(root.val == val) return root;
        TreeNode left = searchBST(root.left,val);
        if(left != null ) return left;
        TreeNode right = searchBST(root.right,val);
        return right;
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode searchBST(TreeNode root, int val) {
        //迭代
        /**
         * 递归与迭代的区别
         * 递归：重复调用函数自身实现循环称为递归；
         * 迭代：利用变量的原值推出新值称为迭代，或者说迭代是函数内某段代码实现循环；
         */
        while (root != null) {
            if(root.val == val) return root;
            else if(root.val < val) root = root.right;
            else if(root.val > val) root = root.left;
        }
        return null;
    }
}