[Leetcode]Kth Smallest Element in a BST

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public class Solution { public int kthSmallest(TreeNode root, int k) { Stack<TreeNode> stack = new Stack<TreeNode>(); TreeNode travel = root; while (root != null){ stack.push(root); root = root.left; } int total = 0; while (!stack.isEmpty()){ total++; TreeNode temp = stack.pop(); if (total == k){ return temp.val; } if (temp.right != null){ temp = temp.right; while (temp!=null){ stack.push(temp); temp = temp.left; } } } return -1; } }