Coding Interview Questions and Answers
Today we are sharing Best 15 Coding Interview Questions and Answers. These are some classic coding interview questions that can help you prepare for your coding interviews. Make sure to practice solving these problems to enhance your problem-solving skills. Here are 15 commonly asked coding interview questions, along with their answers:
1: Reverse a String:
Question: Write a function to reverse a string.
Answer: def reverse_string(s):
return s[::-1]
2: Check for Palindrome:
Question: Write a function to determine if a given string is a palindrome.
Answer: def is_palindrome(s):
return s == s[::-1]
3: Find the Maximum Subarray:
Question: Write a function to find the contiguous subarray with the largest sum.
Answer: def max_subarray(nums):
max_sum = curr_sum = nums[0]
for num in nums[1:]:
curr_sum = max(num, curr_sum + num)
max_sum = max(max_sum, curr_sum)
return max_sum
4: Two Sum Problem:
Question: Given an array of integers, return indices of the two numbers such that they add up to a specific target.
Answer: def two_sum(nums, target):
num_dict = {}
for i, num in enumerate(nums):
complement = target – num
if complement in num_dict:
return [num_dict[complement], i]
num_dict[num] = i
5: Merge Two Sorted Lists:
Question: Merge two sorted linked lists and return it as a new sorted list.
Answer: def merge_two_lists(l1, l2):
if not l1:
return l2
if not l2:
return l1
if l1.val < l2.val:
l1.next = merge_two_lists(l1.next, l2)
return l1
else:
l2.next = merge_two_lists(l1, l2.next)
return l2
6: Reverse Linked List:
Question: Reverse a singly linked list.
Answer: def reverse_linked_list(head):
prev = None
while head:
next_node = head.next
head.next = prev
prev = head
head = next_node
return prev
7: Binary Search:
Question: Implement binary search on a sorted array.
Answer: def binary_search(nums, target):
left, right = 0, len(nums) – 1
while left <= right:
mid = left + (right – left) // 2
if nums[mid] == target:
return mid
elif nums[mid] < target:
left = mid + 1
else:
right = mid – 1
return -1
8: Implement a Stack:
Question: Implement a stack using arrays/lists.
Answer: class Stack:
def __init__(self):
self.stack = []
def push(self, val):
self.stack.append(val)
def pop(self):
if not self.is_empty():
return self.stack.pop()
def is_empty(self):
return len(self.stack) == 0
def peek(self):
if not self.is_empty():
return self.stack[-1]
9: Implement a Queue:
Question: Implement a queue using arrays/lists.
Answer: class Queue:
def __init__(self):
self.queue = []
def enqueue(self, val):
self.queue.append(val)
def dequeue(self):
if not self.is_empty():
return self.queue.pop(0)
def is_empty(self):
return len(self.queue) == 0
def peek(self):
if not self.is_empty():
return self.queue[0]
10: Find the Missing Number:
Question: Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array.
Answer: def missing_number(nums):
n = len(nums)
total_sum = n * (n + 1) // 2
return total_sum – sum(nums)
11: Implement Trie (Prefix Tree):
Question: Implement a trie with insert, search, and startsWith methods.
Answer: class TrieNode:
def __init__(self):
self.children = {}
self.is_end_of_word = False
class Trie:
def __init__(self):
self.root = TrieNode()
def insert(self, word):
node = self.root
for char in word:
if char not in node.children:
node.children[char] = TrieNode()
node = node.children[char]
node.is_end_of_word = True
def search(self, word):
node = self.root
for char in word:
if char not in node.children:
return False
node = node.children[char]
return node.is_end_of_word
def startsWith(self, prefix):
node = self.root
for char in prefix:
if char not in node.children:
return False
node = node.children[char]
return True
12: Check Balanced Parentheses:
Question: Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.
Answer: def is_valid(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
13: Counting Sort:
Question: Implement counting sort algorithm.
Answer: def counting_sort(arr):
max_val = max(arr)
counts = [0] * (max_val + 1)
for num in arr:
counts[num] += 1
sorted_arr = []
for i in range(len(counts)):
sorted_arr.extend([i] * counts[i])
return sorted_arr
14: Find Longest Common Prefix:
Question: Write a function to find the longest common prefix string amongst an array of strings.
Answer: def longest_common_prefix(strs):
if not strs:
return “”
min_str = min(strs, key=len)
for i, char in enumerate(min_str):
for string in strs:
if string[i] != char:
return min_str[:i]
return min_str
15: Rotate Array:
Question: Rotate an array to the right by k steps.
Answer: def rotate(nums, k):
k %= len(nums)
nums[:] = nums[-k:] + nums[:-k]
Conclusion
These questions cover various aspects of data structures and algorithms commonly encountered in coding interviews.