LF.51.Insert In Binary Search Tree

Insert a key in a binary search tree if the binary search tree does not already contain the key. Return the root of the binary search tree.

Assumptions

There are no duplicate keys in the binary search tree

If the key is already existed in the binary search tree, you do not need to do anything

Examples

        5

      /
    3        8

  /
 1     4

insert 11, the tree becomes

        5

      /
    3        8

  /   \
 1     4       11

insert 6, the tree becomes

        5

      /
    3        8

  /   \     /
 1     4   6    11

DFS recursive:

 1 public class Solution {
 2   public TreeNode insert(TreeNode root, int key) {
 3     // Write your solution here
 4     //this is the base case
 5     if (root == null ) {
 6         return new TreeNode(key) ;
 7     }
 8     if (root.key == key){
 9         return root ;
10     }
11     if (root.key > key) {
12         //go to left
13         root.left = insert(root.left, key) ;
14     }
15     if (root.key < key ) {
16         //go to right
17         root.right = insert(root.right, key) ;
18     }
19     //back -> upper -> upper upper to the top then return
20     return root ;
21   }
22 }

since this is called tail recursion, you are recommended to do it in interative: time: O(n) space: O(1)

Interative:

原文地址：https://www.cnblogs.com/davidnyc/p/8655269.html