searchRangeInBinarySearchTree.java

// Source : http://www.lintcode.com/en/problem/search-range-in-binary-search-tree/
// Inspired by : http://www.jiuzhang.com/solutions/search-range-in-binary-search-tree/
// Author : Lei Cao
// Date   : 2015-10-09

/**********************************************************************************
 *
 * Search Range in Binary Search Tree
 *
 * Given two values k1 and k2 (where k1 < k2) and a root pointer to a Binary Search Tree.
 * Find all the keys of tree in range k1 to k2.
 * i.e. print all x such that k1<=x<=k2 and x is a key of given BST.
 * Return all the keys in ascending order.
 *
 * Example:
 *
 * If k1 = 10 and k2 = 22, then your function should return [12, 20, 22].
 *
 *     20
 *    / \
 *   8  22
 *  / \
 * 4  12
 *
 *
 **********************************************************************************/

package searchRangeInBinarySearchTree;

import java.util.ArrayList;

public class searchRangeInBinarySearchTree {
    /**
     * @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> result = new ArrayList<Integer>();
        if (root == null) {
            return result;
        }

        ArrayList<Integer> left = searchRange(root.left, k1, k2);
        ArrayList<Integer> right = searchRange(root.right, k1, k2);

        result.addAll(left);
        if (root.val >= k1 && root.val <= k2) {
            result.add(root.val);
        }
        result.addAll(right);
        return result;
    }

}