How does the frequency counting pattern work for array problems?

The frequency counting pattern builds a hash map where keys are elements and values are their occurrence counts, then uses the counts to answer the question. Walk through the array once to count, then either query the map or iterate it. This solves problems like finding the most frequent element, checking if two strings are anagrams, finding elements that appear more than n divided by k times, or identifying duplicates. Building the frequency map takes O of n time and O of n space.