Search Range in Binary Search Tree

 1 /**
 2  * Definition of TreeNode:
 3  * public class TreeNode {
 4  *     public int val;
 5  *     public TreeNode left, right;
 6  *     public TreeNode(int val) {
 7  *         this.val = val;
 8  *         this.left = this.right = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     /**
14      * @param root: The root of the binary search tree.
15      * @param k1 and k2: range k1 to k2.
16      * @return: Return all keys that k1<=key<=k2 in ascending order.
17      */
18     public ArrayList<Integer> searchRange(TreeNode root, int k1, int k2) {
19         // write your code here
20         ArrayList<Integer> list = new ArrayList<Integer>();
21         if (k1 <= k2) {
22             traverse(root, k1, k2, list);
23         }
24         Collections.sort(list);
25         return list;
26     }
27     
28     public void traverse(TreeNode node, int k1, int k2, ArrayList<Integer> list) {
29         if (node != null) {
30             if (node.val < k1) {
31                 traverse(node.right, k1, k2, list);
32             } else if (node.val > k2) {
33                 traverse(node.left, k1, k2, list);
34             } else {
35                 list.add(node.val);
36                 traverse(node.left, k1, k2, list);
37                 traverse(node.right, k1, k2, list);
38             }
39         }
40     }
41 }