173. 二叉搜索树迭代器

https://leetcode-cn.com/problems/binary-search-tree-iterator/

Java

/*
 * @Author: Goog Tech
 * @Date: 2020-09-02 21:45:01
 * @LastEditTime: 2020-09-02 21:45:29
 * @Description: https://leetcode-cn.com/problems/binary-search-tree-iterator/
 * @FilePath: \leetcode-googtech\#173. Binary Search Tree Iterator\Solution.java
 * @WebSite: https://algorithm.show/
 */

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

class BSTIterator {

    private Stack<TreeNode> stack;

    public BSTIterator(TreeNode root) {
        stack = new Stack<>();
        while(root != null) {
            stack.push(root);
            root = root.left;
        }
    }

    /** @return the next smallest number */
    public int next() {
        TreeNode node = stack.pop();
        int result = node.val;
        if(node.right != null) {
            node = node.right;
            while(node != null) {
                stack.push(node);
                node = node.left;
            }
        }
        return result;
    }

    /** @return whether we have a next smallest number */
    public boolean hasNext() {
        if(stack.isEmpty()) return false;
        return true;
    }
}

/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator obj = new BSTIterator(root);
 * int param_1 = obj.next();
 * boolean param_2 = obj.hasNext();
 */

Python

'''
Author: Goog Tech
Date: 2020-09-02 21:45:08
LastEditTime: 2020-09-02 21:46:17
Description: https://leetcode-cn.com/problems/binary-search-tree-iterator/
FilePath: \leetcode-googtech\#173. Binary Search Tree Iterator\Solution.py
WebSite: https://algorithm.show/
'''

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class BSTIterator(object):

    def __init__(self, root):
        """
        :type root: TreeNode
        """
        self.stack = []
        while root:
            self.stack.append(root)
            root = root.left

    def next(self):
        """
        @return the next smallest number
        :rtype: int
        """
        temp =self.stack.pop()
        result = temp.val
        temp = temp.right
        while temp:
            self.stack.append(temp)
            temp = temp.left
        return result

    def hasNext(self):
        """
        @return whether we have a next smallest number
        :rtype: bool
        """
        return self.stack != []

# Your BSTIterator object will be instantiated and called as such:
# obj = BSTIterator(root)
# param_1 = obj.next()
# param_2 = obj.hasNext()