Cloest Binary Search Tree Value II

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> closestKValues(TreeNode root, double target, int k) {
List<Integer> result = new ArrayList<>();
if (k == 0 || root == null) {
return result;
}

Stack<TreeNode> successor = new Stack<>();
Stack<TreeNode> precessor = new Stack<>();

initialStack(successor, root, true, target);
initialStack(precessor, root, false, target);

if(!successor.isEmpty() && !precessor.isEmpty() && successor.peek().val == precessor.peek().val) {
getNext(precessor, false);
}

while (result.size() < k) {
if (successor.isEmpty()) {
result.add(getNext(precessor, false));
} else if (precessor.isEmpty()) {
result.add(getNext(successor, true));
} else {
boolean sclose = Math.abs((double) successor.peek().val - target) < Math.abs((double)precessor.peek().val - target);
if (sclose) {
result.add(getNext(successor, true));
} else {
result.add(getNext(precessor, false));
}
}
}
return result;
}

private void initialStack(Stack<TreeNode> stack, TreeNode root, boolean successor, double target) {
while (root != null) {
if (root.val == target) {
stack.push(root);
break;
} else if (root.val > target == successor) {
stack.push(root);
root = successor ? root.left : root.right;
} else {
root = successor ? root.right : root.left;
}
}
}

private int getNext(Stack<TreeNode> stack, boolean successor) {
TreeNode current = stack.pop();
int result = current.val;
current = successor ? current.right : current.left;
while (current != null) {
stack.push(current);
current = successor ? current.left : current.right;
}
return result;
}
}