package LeetCode_173
/**
* 173. Binary Search Tree Iterator
* https://leetcode.com/problems/binary-search-tree-iterator/description/
*
* Implement an iterator over a binary search tree (BST).
* Your iterator will be initialized with the root node of a BST.
Calling next() will return the next smallest number in the BST.
Note:
next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
You may assume that next() call will always be valid, that is,
there will be at least a next smallest number in the BST when next() is called.
* */
class TreeNode(var `val`: Int) {
var left: TreeNode? = null
var right: TreeNode? = null
}
/*
* solution: in-order + ArrayList
* */
class BSTIterator(root: TreeNode?) {
val list = ArrayList<Int>()
init {
inorder(root)
}
//inorder:left->root->right, save sorted numbers in list，is Ascending
private fun inorder(root:TreeNode?){
if (root==null){
return
}
inorder(root.left)
list.add(root.`val`)
inorder(root.right)
}
/** @return the next smallest number */
fun next(): Int {
return list.removeAt(0)
}
/** @return whether we have a next smallest number */
fun hasNext(): Boolean {
return list.isNotEmpty()
}
}
/**
* Your BSTIterator object will be instantiated and called as such:
* var obj = BSTIterator(root)
* var param_1 = obj.next()
* var param_2 = obj.hasNext()
*/
