1 /** 2  * Definition for a binary tree node. 3  * public class TreeNode { 4  *     int val; 5  *     TreeNode left; 6  *     TreeNode right; 7  *     TreeNode(int x) { val = x; } 8  * } 9  */10 public class Solution {11     public List
     
       closestKValues(TreeNode root, double target, int k) {12         List
      
        result = new ArrayList<>();13         if (k == 0 || root == null) {14             return result;15         }16         17         Stack
       
         successor = new Stack<>();18         Stack
        
          precessor = new Stack<>();19         20         initialStack(successor, root, true, target);21         initialStack(precessor, root, false, target);22         23         if(!successor.isEmpty() && !precessor.isEmpty() && successor.peek().val == precessor.peek().val) {24             getNext(precessor, false);25         }26         27         while (result.size() < k) {28             if (successor.isEmpty()) {29                 result.add(getNext(precessor, false));30             } else if (precessor.isEmpty()) {31                 result.add(getNext(successor, true));32             } else {33                 boolean sclose = Math.abs((double) successor.peek().val - target) < Math.abs((double)precessor.peek().val - target);34                 if (sclose) {35                     result.add(getNext(successor, true));36                 } else {37                     result.add(getNext(precessor, false));38                 }39             }40         }41         return result;42     }43     44     private void initialStack(Stack
         
           stack, TreeNode root, boolean successor, double target) {45         while (root != null) {46             if (root.val == target) {47                 stack.push(root);48                 break;49             } else if (root.val > target == successor) {50                 stack.push(root);51                 root = successor ? root.left : root.right;52             } else {53                 root = successor ? root.right : root.left;54             }55         }56     }57     58     private int getNext(Stack
          
            stack, boolean successor) {59 TreeNode current = stack.pop();60 int result = current.val;61 current = successor ? current.right : current.left;62 while (current != null) {63 stack.push(current);64 current = successor ? current.left : current.right;65 }66 return result;67 }68 }