LC 1128. Number of Equivalent Domino Pairs

A concise tl;dr to speed up your coding interview prep

Number of Equivalent Domino Pairs — Counting pairs using frequency map

LeetCode

Problem TL;DR

Count number of equivalent domino pairs (order doesn’t matter).

Solution TL;DR

• Use sorted tuple (a, b) as hash key into hash map

• Count pairs using combination formula count * (count - 1) // 2