Lunski's Clutter

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

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Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

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Input: "race a car"
Output: false

Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

Example 1:

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Input: [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
             Not 7-1 = 6, as selling price needs to be larger than buying price.

Example 2:

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Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree.

Example 1:

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Input: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
Output: [3,9,20,null,null,15,7]

Example 2:

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Input: preorder = [-1], inorder = [-1]
Output: [-1]

Given a binary tree, collect a tree’s nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.

Example:

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Input: [1,2,3,4,5]
  
          1
         / \
        2   3
       / \     
      4   5    

Output: [[4,5,3],[2],[1]]

Explanation:

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1. Removing the leaves [4,5,3] would result in this tree:

          1
         / 
        2          
 

2. Now removing the leaf [2] would result in this tree:

          1          
 

3. Now removing the leaf [1] would result in the empty tree:

          []        

Given the root of a binary tree, return its maximum depth.

A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1:

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Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:

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Input: root = [1,null,2]
Output: 2

Example 3:

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Input: root = []
Output: 0

Example 4:

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Input: root = [0]
Output: 1