Minimum Rounds to Complete Tasks

Problem

Given task difficulty levels, return the minimum number of rounds to complete all tasks, where each round completes either 2 or 3 tasks of the same level, or -1 if any level appears exactly once.

For a level with count c the minimum rounds is (c + 2) // 3, which prefers groups of three. Any singleton makes the schedule impossible.

Hint

Counts of 2 and 3 take one round, and every larger count can be built from 2s and 3s.

Test cases

case 1

in: [[2,2,3,3,2,4,4,4,4,4]]

expected: 4

case 2

in: [[5,5,5,5]]

expected: 2

case 3

in: [[2,3,3]]

expected: -1

case 4

in: [[7,7,7,7,7,7]]

expected: 2

case 5

in: [[1]]

expected: -1

Starter codePython

def min_rounds_tasks(tasks):
    # Your code here
    pass

5 test cases · run your code against them in the editor