Takeaways

• A Map / Dictionary / HashTable is an unordered collection of Key-value pairs
• Keys should be unique, and should be an immutable data type (string, int, double)
• A hash function takes a key value, and maps to a "bucket" in O(1) time
• A hash table is just an array, where each spot in the array is a "bucket"
• A hash collision may occur if two keys map to the same bucket
• The key set/key space is the set of keys in a hash table
• Insertions and lookups happen in O(1) time (assuming key value is known and no hash collisions occur)
• The Hash table library in java is called HashMap
• HashMap documentation: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html


• A HashSet<> is a Set data type that uses a HashMap under the hood
• A set is a unordered collection of data with no duplicates
• HashSets have O(1) insertions, lookups, and removals

Code

• February 11th Code
• February 13th Code