Hashing Patterns (capstone)

The hash map is the LeetCode swiss-army knife

Most 'medium' array/string problems come down to one of three hash-map moves:

• Frequency counts: how many times does each item appear? (collections.Counter)

• Grouping by a canonical key: bucket items that share some derived key. (collections.defaultdict(list))

• Seen-sets: have I encountered this before? (a plain set, as in Two Sum and graph traversals)