LF.52.Search in Binary Search Tree

Find the target key K in the given binary search tree, return the node that contains the key if K is found, otherwise return null.

对于 tail recursion  的， 都是可以换成iterative, 把栈空间换成堆空间

   //recursive: time: o(h) space: o(h)
  public TreeNode search(TreeNode root, int key) {
    // Write your solution here.
    if (root == null ) {
        return root ;
    }
    if (root.key == key) {
        return root ;
    }
    else if (root.key < key) {
        return search(root.right, key);
    } else {
        return search(root.left, key);
    }
  }

  /*iterative way of doing: time: o(h) space: o(1)
    this is tail recursion: recursion happens at the last statement
  */
    public TreeNode search_iter(TreeNode root, int key){
        if (root == null) {
            return root ;
        }
        TreeNode curr = root ;
        //very like linked list.
        while(curr != null){
            if (curr.key == key) {
                break ;
            } else if (curr.key < key ) {
                curr = curr.right ;
            } else {
                curr = curr.left ;
            }
        }
        return curr ;
    }