11

2017.9.14

二叉搜索树的前序遍历就是有序数列。

/** * 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: param root: The root of the binary search tree     * @param k1: An integer     * @param k2: An integer     * @return: return: Return all keys that k1<=key<=k2 in ascending order     */    public List<Integer> searchRange(TreeNode root, int k1, int k2) {        // write your code here LinkedList<Integer> res = new LinkedList<Integer>(); if(root == null){ return res; } // 其实也就是二叉树的前序遍历。 LinkedList<TreeNode> stack = new LinkedList<TreeNode>(); TreeNode bt = root; while(bt != null || !stack.isEmpty()){ while(bt !=null){ stack.push(bt); bt = bt.left; } bt = stack.pop(); if(bt.val > k2){ return res; } if(bt.val >= k1){ res.add(bt.val); } bt = bt.right; } return res; }}