FAANG / Big Tech · 15 Problems

Top Data Structures & Algorithms Coding Interview Problems

Study the most recurring coding patterns tested during Big Tech and high-growth startup engineering interviews.

Q1 Easy

Two Sum: Find two numbers in an array that add up to a target sum.

Use a Hash Map to record previously seen numbers and their indices, achieving O(n) time complexity.

Solution Code 
def two_sum(nums, target):
    seen = {} # value -> index
    for i, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], i]
        seen[num] = i
    return []

# Test: nums = [2, 7, 11, 15], target = 9 -> [0, 1]
Q2 Easy

Reverse a Singly Linked List in place.

Iterate through the list while maintaining previous, current, and next pointers.

Solution Code 
def reverse_list(head):
    prev = None
    curr = head
    while curr:
        next_temp = curr.next
        curr.next = prev
        prev = curr
        curr = next_temp
    return prev # New head

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