555.py

"""
QUESTION 1:
========================================================================================================
Give a list of numbers, write a function to find the maximum number in the list.
Note: For the purpose of this problem, we define empty list will return None.

NOTE: DO NOT USE "MAX" KEYWORD. WRITE algorithm using loop.

Example 1:
========================================
Input: [10, 5, 20, 15, 25]
Output: 25
Example 2:
========================================
Input:[10,10,10]
Output: 10
Example 3:
========================================
Input: []
Output: None
"""

def find_maximum(numbers):
    if numbers is None:
        return None
    max_number = numbers[0]
    for i in numbers:
        if i > max_number:
            max_number = i
    return max_number



"""
QUESTION 2:
========================================================================================================
Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
Write a function named generateParenthesis that takes an integer as an input and returns a list of strings
as an output. Note that you can define a function inside a function if necessary.
Example 1:
========================================
Input: 0
Output: ['']
Example 2:
========================================
Input: 1
Output: ['()']
Example 3:
========================================
Input: 2
Output: ['(())', '()()']
Example 4:
========================================
Input: 3
Output: ['((()))', '(()())', '(())()', '()(())', '()()()'])
"""

def generateParenthesis(n):
    def backtrack(res, curr, open_count, close_count, max_pairs):
        if len(curr) == max_pairs * 2:
            res.append(curr)
            return
        if open_count < max_pairs:
            backtrack(res, curr + '(', open_count + 1, close_count, max_pairs)
        if close_count < open_count:
            backtrack(res, curr + ')', open_count, close_count + 1, max_pairs)

    res = []
    backtrack(res, '', 0, 0, n)
    return res


"""
QUESTION 3:
========================================================================================================
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:
========================================
Input: "A man, a plan, a canal: Panama"
Output: true

Explanation:
After removing non-alphanumeric charactors and ignoring cases, the input is:  amanaplanacanalPanama
which reads the same as backward and forward, so it is true.

Example 2:
=========================================
Input: "race a car"
Output: false
Write a function named isPalindrome that takes a string as an input and returns a bool as an output.

Explanation:
After removing non-alphanumeric charactors and ignoring cases, the input is:  raceacar
which does not read the same as backward and forward, so it is false.
"""

def isPalindrome(x):
    # Convert the string to lowercase and remove non-alphanumeric characters
    x = ''.join(e for e in x.lower() if e.isalnum())
    # Check if the string is equal to its reverse
    return x == x[::-1]