Hash maps

A hash map stores a value under a key and finds it without scanning the whole collection. These articles explain the hash that chooses a bucket, what happens when two keys land in the same bucket, and the frequency count the lessons use to answer how many times a value appears.

How a Hash Map Remembers What You Have Already Seen
A hash map associates unique keys with values. Expected O(1) lookup can replace a repeated scan, as the one-pass Two Sum algorithm demonstrates.
What Is a Hash Collision? Why O(1) Is Only Expected
A collision occurs when distinct keys select the same bucket. Correct collision resolution preserves results but can increase lookup time.
What Is a Frequency Count? Tallying Values in One Pass
A frequency count stores how many times each value has appeared. One pass updates the tally, and a tie keeps the value that showed up first.