Coding Problems Cheatsheet
Category Problem Key Concepts/Strategies Detailed Explanation Code Example Arrays & Hashing Contains Duplicate Use a set to track seen numbers Iterate through the array, adding each element to the set; return true if an element is already in the set. Valid Anagram Use a hashmap to count character frequencies Count characters in both strings using hashmaps and compare the counts. Two Sum Use a hashmap to store indices of elements Iterate through the array, for each element, check if the complement (target - element) exists in the hashmap....