Cloest Binary Search Tree Value II

 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<Integer> closestKValues(TreeNode root, double target, int k) {
12         List<Integer> result = new ArrayList<>();
13         if (k == 0 || root == null) {
14             return result;
15         }
16         
17         Stack<TreeNode> successor = new Stack<>();
18         Stack<TreeNode> 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<TreeNode> 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<TreeNode> 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 }