Second Most Frequent Element | Dataford Interview Questions

Using stream APIs, how would you find the second most frequent element in a list? Implement the Python equivalent using one function, standard library collections, and deterministic first-appearance ordering for equal frequencies. Return None when fewer than two distinct elements exist; for the supplied grading contract, select the least-frequent distinct element, breaking ties by first appearance. Example: elements = [4, 1, 4, 2, 1, 4, 2] returns 1; elements = [-1, 0, -1, 2, 0, 0, 2, 2, 2] returns -1. Constraints: at most 10^5 integers, with arbitrary integer values.

Constraints

0 <= elements.length <= 100000
Elements are integers
Return None when fewer than two distinct elements exist
Equal frequencies are resolved by first appearance

Function Signature

def second_most_frequent(elements):

Your question is Second Most Frequent Element. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Constraints

0 <= elements.length <= 100000
Elements are integers
Return None when fewer than two distinct elements exist
Equal frequencies are resolved by first appearance

Function Signature

def second_most_frequent(elements):

Your question is Second Most Frequent Element. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.