题目

给定一棵二叉查找树和一个新的树节点，将节点插入到树中。
你需要保证该树仍然是一棵二叉查找树。

分析

分别用递归和非递归两种方法实现。本质上会发现，两种方法类似

public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        if(root == null)
            return node;
            
        if(root.val > node.val)
            root.left = insertNode(root.left, node);
        else
            root.right = insertNode(root.right, node);
        
        return root;
    }
}

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        // write your code here
        if (root == null) {
            root = node;
            return root;
        }
        TreeNode tmp = root;
        TreeNode last = null;
        while (tmp != null) {
            last = tmp;
            if (tmp.val > node.val) {
                tmp = tmp.left;
            } else {
                tmp = tmp.right;
            }
        }
        if (last != null) {
            if (last.val > node.val) {
                last.left = node;
            } else {
                last.right = node;
            }
        }
        return root; 
    }
}