Arrays Interview Questions and Patterns

Why Arrays Matter

Arrays show up in almost every interview. The same few patterns repeat: two pointers, sliding window, prefix sum, and in-place manipulation.

Two Pointers

Sorted array

• Two Sum, Three Sum, Four Sum—fix one or two and move pointers.
• Remove duplicates in-place.

Opposite ends

• Container with most water.
• Valid palindrome.

Sliding Window

Fixed size

• Max sum of subarray of size K.
• First negative in every window of size K.

Variable size

• Longest substring with K distinct characters.
• Minimum size subarray sum.

Prefix Sum and Hashing

Subarray sum

• Prefix sum for range sum in O(1).
• Hash map for "find subarray with sum equal to target."

In-Place Tricks

• Move zeros: two pointers, swap.
• Dutch national flag: three-way partition.

Summary

Recognize the pattern from the problem statement, then code the template. Use Preplume(/) to practice array problems by pattern.