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 =10and k2 =22, then your function should return[12, 20, 22].

    20
   /  \
  8   22
 / \
4   12

分析

分治法

    public List<Integer> searchRange(TreeNode root, int k1, int k2) {
        // write your code here
        List<Integer> ret = new ArrayList<Integer>();
        if(root == null)
            return ret;

        List<Integer> left = searchRange(root.left, k1, k2);
        List<Integer> right = searchRange(root.right, k1, k2);
        ret.addAll(left);
        if(root.val >= k1 && root.val <= k2){
            ret.add(root.val);
        }
        ret.addAll(right);
        return ret;
    }