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Top 10 Coding Interview Questions You Need to Master

November 12, 2024
byTechX
0
Interview Interview

Landing a job at a top tech company like Amazon, Google, or Microsoft in 2024 requires not only strong programming skills but also the ability to solve complex coding challenges under time pressure. In this blog, we’ll walk you through the top 10 coding interview questions that are commonly asked in technical interviews and provide tips on how to ace them. By mastering these questions, you’ll be ready for your next coding interview.

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1. Reverse a String

One of the most classic coding interview questions, reversing a string, tests your understanding of string manipulation and algorithms. This question is a favorite because it can be solved using different approaches, and interviewers want to see if you can optimize your solution.

Approach:

  • Naive solution: Convert the string into a list and reverse it.
  • Optimal solution: Use a two-pointer approach to reverse the string in-place without extra space.

Example:

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

2. Find the Missing Number

Given an array of size n-1 containing numbers from 1 to n, find the missing number. This question assesses your problem-solving and mathematical thinking skills.

Approach:

  • Mathematical approach: Use the formula for the sum of the first n natural numbers to find the missing number.
  • Optimal time complexity: O(n).

Example:

python
def find_missing_number(nums):
n = len(nums) + 1
total = n * (n + 1) // 2
return total - sum(nums)

3. Two Sum Problem

The Two Sum problem is commonly asked in tech interviews. You’re given an array and a target number, and you need to find two numbers in the array that sum up to the target.

Approach:

  • Use a hash map to store the difference between the target and the current number as you iterate through the array.
  • Check if the number exists in the hash map.

Example:

python
def two_sum(nums, target):
seen = {}
for i, num in enumerate(nums):
complement = target - num
if complement in seen:
return [seen[complement], i]
seen[num] = i

4. Palindrome Check

This question asks you to determine whether a string is a palindrome (it reads the same forward and backward). This problem tests string manipulation and understanding of algorithms.

Approach:

  • Compare characters from the front and back of the string to check if they are equal.
  • Use the two-pointer technique for an efficient solution.

Example:

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

5. Longest Substring Without Repeating Characters

This is a common problem in interviews that assesses your ability to work with sliding windows and hash maps. You need to find the longest substring in a given string without repeating characters.

Approach:

  • Use a sliding window and a hash map to store the last seen index of characters.
  • Update the window size dynamically as you encounter repeating characters.

Example:

python
def length_of_longest_substring(s):
window = {}
left = 0
max_length = 0
for right, char in enumerate(s):
if char in window:
left = max(left, window[char] + 1)
window[char] = right
max_length = max(max_length, right - left + 1)
return max_length

6. Merge Intervals

You’re given a collection of intervals and asked to merge overlapping intervals. This problem tests your ability to work with intervals and sorting.

Approach:

  • Sort intervals by start time.
  • Iterate through the intervals and merge them if they overlap.

Example:

python
def merge_intervals(intervals):
intervals.sort(key=lambda x: x[0])
merged = []
for interval in intervals:
if not merged or merged[-1][1] < interval[0]:
merged.append(interval)
else:
merged[-1][1] = max(merged[-1][1], interval[1])
return merged

7. Find the Longest Common Prefix

This question tests your string manipulation skills. You’re given a list of strings and need to find the longest common prefix (if any).

Approach:

  • Start by comparing the first two strings in the list and find the common prefix.
  • Iterate through the rest of the strings and keep updating the common prefix.

Example:

python
def longest_common_prefix(strs):
if not strs:
return ""
prefix = strs[0]
for s in strs[1:]:
while not s.startswith(prefix):
prefix = prefix[:-1]
return prefix

8. Valid Anagram

This question asks you to determine if two strings are anagrams of each other, meaning they contain the same characters in the same frequency.

Approach:

  • Sort both strings and compare them.
  • Alternatively, use a hash map to count the frequency of each character.

Example:

python
def is_anagram(s, t):
return sorted(s) == sorted(t)

9. Maximum Subarray Sum (Kadane’s Algorithm)

Finding the maximum sum of a contiguous subarray is a typical dynamic programming problem. This question assesses your understanding of Kadane’s Algorithm.

Approach:

  • Use dynamic programming to keep track of the current maximum subarray sum and update the global maximum.

Example:

python
def max_subarray_sum(nums):
current_sum = max_sum = nums[0]
for num in nums[1:]:
current_sum = max(num, current_sum + num)
max_sum = max(max_sum, current_sum)
return max_sum

10. Balanced Parentheses

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, you need to determine if the input string is valid (i.e., parentheses must close in the correct order).

Approach:

  • Use a stack to keep track of opening brackets and ensure each closing bracket matches the most recent opening bracket.

Example:

python
def is_valid_parentheses(s):
stack = []
mapping = {')': '(', '}': '{', ']': '['}
for char in s:
if char in mapping:
top_element = stack.pop() if stack else '#'
if mapping[char] != top_element:
return False
else:
stack.append(char)
return not stack

Conclusion

Mastering these top 10 coding interview questions will put you on the path to success in your technical interviews. Be sure to practice these problems thoroughly and understand the underlying concepts, as interviewers look for your problem-solving approach and code optimization skills. With consistent practice and the right mindset, you’ll be able to confidently tackle any coding interview challenge that comes your way.

By practicing these common coding interview questions and honing your skills, you can boost your chances of landing your dream tech job. For more in-depth preparation and mock interviews, check out resources like Interview Sidekick and Google Interview Warmup. Happy coding!

November 12, 2024
byTechX
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