package LeetCode_285
import java.util.*
/**
* 285. Inorder Successor in BST
* (Prime)
*
Given a binary search tree and a node in it, find the in-order successor of that node in the BST.
The successor of a node p is the node with the smallest key greater than p.val.
Example 1:
Input: root = [2,1,3], p = 1
Output: 2
Explanation: 1's in-order successor node is 2. Note that both p and the return value is of TreeNode type.
Example 2:
Input: root = [5,3,6,2,4,null,null,1], p = 6
Output: null
Explanation: There is no in-order successor of the current node, so the answer is null.
Note:
If the given node has no in-order successor in the tree, return null.
It's guaranteed that the values of the tree are unique.
*/
class TreeNode(var `val`: Int) {
var left: TreeNode? = null
var right: TreeNode? = null
}
//inorder: root->left->right
class Solution {
fun inorderSuccessor(root_: TreeNode?, node: TreeNode): TreeNode? {
var findIt = false
var root = root_
val stack = Stack<TreeNode>()
stack.push(root)
while (root != null || stack.size > 0) {
if (root != null) {
stack.push(root)
root = root.left!!
} else {
root = stack.pop()
if (findIt) {
return root
}
if (root.`val` == node.`val`) {
//if found the node, the next node is the result
//because next node is current node's Successor
findIt = true
}
root = root.right
}
}
return null
}
}