Maps

Java's Map Interface

Practice for Java Maps

Here are two practice links on Coding Bat to see if you understand how to use the Java Map class.

1. 1. https://codingbat.com/java/Map-1

   2. https://codingbat.com/java/Map-2

More Practice with Maps

Here are some harder LeetCode problems that can be solved using Maps.

1. Roman Numerals

Practice on LeetCode: Using a Map as a Frequency Counter

One common way to use a Map is to count the number of occurrences of items. When an item is being processed, we check to see if it is already in the Map. If it is not, we add it to the Map and set its frequency (value field) to 1. If it is already in the Map, we simply increment its frequency count in the value field.

Use this strategy to solve the following LeetCode problem. First, go through the string and create a map with the frequencies of each letter. Then parse the string a second time until you find a letter with a frequency of 1. Return that letter.

LeetCode Problem: First-Unique-Character-In-A-String

LeetCode Problem: Map-Sum-Pairs

Enignma Project (Hard)

Do the It's an Enigma problem from the 2018 Lockheed Martin Project. This problem is challenging. Ask your instructor for starter code.