LintCode 二叉查找树中搜索区间题目代码

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/**
 * 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>   results = new ArrayList<Integer>();
        dfs(root, k1, k2,results);
        //Collections.reverse(results);
        return results;
    }
    
    private void dfs(TreeNode root, int k1, int k2, ArrayList<Integer> res) {
        
        if(root == null)
            return;
        
        if(root.val > k1) {
            dfs(root.left,k1,k2,res);
        }
        
        if(root.val >=k1 && root.val <=k2) {
            res.add(root.val);
        }
        
        if(root.val < k2)
            dfs(root.right,k1,k2,res);
        
    }
}