Two Pointers Questions at Yahoo: What to Expect

Two Pointers questions appear in about 14% of Yahoo's coding problems, making them a core technique you must master. While not as dominant as Hash Table or Array questions, their presence is significant and consistent. This frequency indicates Yahoo's interviewers value candidates who can write efficient, in-place solutions for problems involving sequences—often strings, arrays, or linked lists. Mastering this pattern demonstrates you can move beyond brute-force approaches and think critically about optimizing time and space complexity, a key skill for the scalable systems Yahoo builds.

What to Expect — Types of Problems

Yahoo's Two Pointers problems typically fall into three categories. First, opposite-direction pointers are used for problems like finding a pair with a target sum in a sorted array or checking if a string is a palindrome. Second, same-direction (fast & slow) pointers are common in cycle detection within linked lists or finding a specific node. Third, sliding window variants often appear for finding subarrays or substrings that meet a condition, such as the longest substring without repeating characters. You can expect these problems to be framed around real-world data processing scenarios, like filtering logs, validating user input sequences, or optimizing data streams.

How to Prepare — Study Tips with One Code Example

Focus on the underlying pattern, not memorization. Start by identifying the classic use cases: sorted arrays often use opposite-end pointers, while linked lists and sequential scans use fast/slow or sliding windows. Always clarify input properties (e.g., "Is the array sorted?") as this dictates the approach. Practice writing clean, bug-free iterations—off-by-one errors are common.

A fundamental pattern is the opposite-direction two-pointer sum check. Here is the implementation for finding if a sorted array contains two numbers that sum to a target.

def has_target_sum(nums, target):
    left, right = 0, len(nums) - 1
    while left < right:
        current_sum = nums[left] + nums[right]
        if current_sum == target:
            return True
        elif current_sum < target:
            left += 1
        else:
            right -= 1
    return False

Recommended Practice Order

Build competency progressively. First, master classic opposite-direction problems like Two Sum II (sorted array) and Valid Palindrome. Second, tackle fast/slow pointer problems like Linked List Cycle and Middle of the Linked List. Third, move to sliding window problems, starting with fixed-size windows before attempting variable-size ones like Longest Substring Without Repeating Characters. Finally, solve Yahoo's tagged problems to familiarize yourself with their specific phrasing and constraints.

Practice Two Pointers at Yahoo