Common Array & String Problems

Arrays and strings are regularly featured in coding interviews and programming problems. Below are many of the common problems you need to master with explanations.

Array Problems

• Find Maximum/Minimum Element: Determine the largest or smallest number in an array.
• Searching: Check if a given element exists within the array.
• Duplicate Elements: Detect if the array has any duplicate values.
• Move Zeroes: Move all zeroes in an array to the end while maintaining the order of other elements.
• Rotate Array: Rotate the elements of the array by a certain number of positions.
• Subarray Problems: Find subarrays with maximum sum, product, or specific properties.

String Problems

• Palindrome Checking: Verify if a string reads the same backwards.
• Anagram Detection: Check if two strings are anagrams of each other.
• Substring Search: Find whether a substring exists inside a larger string.
• Reversing Strings: Reverse the order of characters in a string.
• Longest Substring Without Repeating Characters: Find the maximum length substring with all unique characters.

Sample Problem: Move Zeroes (Array)

def moveZeroes(nums):
    j = 0  # index for placing non-zero
    for i in range(len(nums)):
        if nums[i] != 0:
            nums[j] = nums[i]
            if i != j:
                nums[i] = 0
            j += 1

Sample Problem: Check Palindrome (String)

def isPalindrome(s):
    return s == s[::-1]

Tips for Problem Solving:

• Understand constraints and edge cases such as empty arrays or strings.
• Choose brute force first, then optimize (using hashing, two-pointer or sliding window techniques).
• Practice coding these common problems repeatedly to build familiarity.