Day 22 - Tricky String & Array Problems

Reverse a String without using built-in functions

def reverse_string(s):
    return s[::-1]

print(reverse_string("ShaiviConnect"))  # tcennoCiviahS
          

Check if a String is a Palindrome

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

print(is_palindrome("madam"))  # True
          

Find the First Non-Repeating Character

from collections import Counter

def first_non_repeating(s):
    count = Counter(s)
    for char in s:
        if count[char] == 1:
            return char
    return None

print(first_non_repeating("aabbcde"))  # c
          

Check if Two Strings are Anagrams

def are_anagrams(s1, s2):
    return sorted(s1) == sorted(s2)

print(are_anagrams("listen", "silent"))  # True
          

Find Missing Number in an Array

def missing_number(arr, n):
    total = n * (n + 1) // 2
    return total - sum(arr)

print(missing_number([1, 2, 4, 5], 5))  # 3
          

Find Duplicate in an Array

def find_duplicate(arr):
    seen = set()
    for num in arr:
        if num in seen:
            return num
        seen.add(num)
    return None

print(find_duplicate([1, 2, 3, 4, 2]))  # 2
          

Rotate an Array by K steps

def rotate_array(arr, k):
    k = k % len(arr)
    return arr[-k:] + arr[:-k]

print(rotate_array([1, 2, 3, 4, 5], 2))  # [4, 5, 1, 2, 3]
          

Find Maximum Subarray Sum (Kadane's Algorithm)

def max_subarray_sum(arr):
    max_current = max_global = arr[0]
    for num in arr[1:]:
        max_current = max(num, max_current + num)
        if max_current > max_global:
            max_global = max_current
    return max_global

print(max_subarray_sum([-2,1,-3,4,-1,2,1,-5,4]))  # 6
          

✅ Key Takeaways

💡

Mastering tricky problems builds strong problem-solving ability and algorithmic thinking.

⚡

Always optimize your solutions - Kadane's Algorithm achieves O(n) time complexity.

🎯

String & Array questions are fundamental and appear in almost every technical interview.

Tricky String & Array Problems

📌 Interview Questions & Solutions