85. Insert Node in a Binary Search Tree【easy】

Given a binary search tree and a new tree node, insert the node into the tree. You should keep the tree still be a valid binary search tree.

Notice

You can assume there is no duplicate values in this tree + node.

 

Example

Given binary search tree as follow, after Insert node 6, the tree should be:

  2             2
 / \           / \
1   4   -->   1   4
   /             / \
  3             3   6

Challenge

Can you do it without recursion?

解法一：

 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;
     }
 }

解法二：

 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) {
             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;
     }
 }

解法三：

 class Solution {
 public:
     /*
      * @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.
      */
     TreeNode * insertNode(TreeNode * root, TreeNode * node) {
         stack<TreeNode * > sta;
         sta.push(root);
         TreeNode * last = NULL;
         while (sta.size() != ) {
             TreeNode * now = sta.top();
             sta.pop();
             if (now == NULL) {
                 if (last == NULL) {
                     root = node;
                 } else if (last->val <= node->val) {
                     last -> right = node;
                 } else {
                     last -> left = node;
                 }
                 break;
             } else if (now->val <= node->val) {
                 sta.push(now->right);
             } else {
                 sta.push(now->left);
             }
             last = now;
         }
         return root;
     }
 };

参考@DLNU-linglian 的代码