11 - 二叉查找树中搜索区间

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;
}
}