Arrays and strings

Arrays

Array is a fixed or dynamic collection of values stored in index order.

Important questions

• Two Sum
• Best Time to Buy and Sell Stock
• Contains Duplicate
• Product of Array Except Self
• Maximum Subarray
• Merge Intervals
• Rotate Array
• Move Zeroes

String patterns

• Valid Palindrome
• Longest Substring Without Repeating Characters
• Group Anagrams
• String Anagram Check
• Reverse Words in a String
• Longest Common Prefix

Common patterns

• Two pointers
• Sliding window
• Prefix/suffix sums
• Hash map for frequency

Example interview answer

“Since we need to check matches efficiently, I would use a hash map to count frequencies and compare. This reduces repeated scanning and gives O(n) time.”