285. Inorder Successor in BST
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 } }