BST range query.java

/**
 * 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.
     */
    public ArrayList<Integer> searchRange(TreeNode root, int k1, int k2) {
        ArrayList<Integer> res = new ArrayList<Integer>();
        searchRange(res, root, k1, k2);
        return res;
    }
    
    private void searchRange(ArrayList<Integer> res, TreeNode root, int k1, int k2) {
        if (root == null)
            return;
        if (k2 < root.val) {
            searchRange(res, root.left, k1, k2);
            return;
        }
        if (k1 > root.val) {
            searchRange(res, root.right, k1, k2);
            return;
        }
        if (k1 == Integer.MIN_VALUE) {
            searchRange(res, root.left, k1, k2);
            if (k2 >= root.val) {
                res.add(root.val);
                searchRange(res, root.right, k1, k2);
            }
            return;
        }
        if (k2 == Integer.MAX_VALUE) {
            if (k1 <= root.val) {
                searchRange(res, root.left, k1, k2);
                res.add(root.val);
            }
            searchRange(res, root.right, k1, k2);
            return;
        }
        searchRange(res, root.left, k1, Integer.MAX_VALUE);
        res.add(root.val);
        searchRange(res, root.right, Integer.MIN_VALUE, k2);
    }
}