LintCode-11.二叉查找树中搜索区间

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param k1 and k2: range k1 to k2.
     * @return: Return all keys that k1<=key<=k2 in ascending order.
     */
    ArrayList<Integer> result = new ArrayList<Integer>();
    public ArrayList<Integer> searchRange(TreeNode root, int k1, int k2) {
        // write your code here
        if(root == null) return result;
        if(root.val >= k1 && root.val <= k2){
            result.add(root.val);
            searchRange(root.left, k1, k2);
            searchRange(root.right, k1, k2);
        }
        else if(root.val < k1){
            searchRange(root.right, k1, k2);
        }
        else if(root.val > k2){
            searchRange(root.left, k1, k2);
        }
        Collections.sort(result);
        return result;
    }
}