Binary Tree Paths

Given a binary tree, return all root-to-leaf paths. Note: A leaf is a node with no children. Example Input: 1 / \ 2 3 \ 5 Output: ["1->2->5", "1->3"] Explanation: All root-to-leaf paths are: 1->2->5, 1->3 Solution # Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def binaryTreePaths(self, root): """ :type root: TreeNode :rtype: List[str] """ res = [] def traverse(root, path): if root == None: return path += str(root.

by lek tin in "algorithm" access_time 1-min read

Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level). Example Given binary tree `[3,9,20,null,null,15,7]`, 3 / \ 9 20 / \ 15 7 return its level order traversal as: [ [3], [9,20], [15,7] ] Solution (recursion) # Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.

by lek tin in "algorithm" access_time 1-min read

Binary Tree Level Order Traversal II

Given a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root). For example: Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7 return its bottom-up level order traversal as: [ [15,7], [9,20], [3] ] Solution # Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.

by lek tin in "algorithm" access_time 1-min read

Binary Search Tree Iterator

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. Calling next() will return the next smallest number in the BST. Note next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree. Solution # Definition for a binary tree node # class TreeNode(object): # def __init__(self, x): # self.

by lek tin in "algorithm" access_time 1-min read