Postage drawer: Even-key census
Inputs
readings is a list of integers (numbers with no decimal part). It may be empty, and numbers may repeat unless task 1 says otherwise.
Your tasks
- Create a list
fewestStamps. Each number inreadingsis an amount of postage. You can use as many stamps of value 1, 4, or 9 as you need. Find the fewest stamps whose values add up to each amount exactly. For amount 8, two stamps of value 4 are enough. Amount 0 needs 0 stamps. Put the answers in input order. - Count the even numbers in
fewestStamps. Store the count inevenCount. A number is even when it divides by 2 with no remainder. - Complete
postageDrawerEvenKeyCensusso it returnsevenCount. Return it, do not print it.
Example
If readings is [4, 7, 4, 4, 6], then fewestStamps is [1, 4, 1, 1, 3] and postageDrawerEvenKeyCensus returns 1.
Rules
- 0 counts as an even number.
- If
fewestStampsis empty, return 0.
Test data
TEST DATA 1: readings is [0, 9, 9, 8, 14].
TEST DATA 2: readings is [7, 8, 8, 8].
Examples
Input: readings = [0,9,9,8,14] Output: 2
fewestStamps is [0, 1, 1, 2, 3]. The even numbers are [0, 2]. There are 2, so return 2.
Input: readings = [7,8,8,8] Output: 4
fewestStamps is [4, 2, 2, 2]. The even numbers are [4, 2, 2, 2]. There are 4, so return 4.
Input: readings = [] Output: 0
fewestStamps is []. The even numbers are []. There are 0, so return 0.
Input limits
- 0 <= input size <= 64.
- Answers fit in a signed 32-bit integer: -2,147,483,648 through 2,147,483,647.
- Input numbers are whole numbers from 0 through 40.
Efficiency goal
Big-O describes how the work or memory needed grows as the input gets larger.
Efficiency goal: time O(n + M); extra memory, including the helper list, O(n). n is the input length; M is the largest input number. These labels describe how work and memory grow with the input.
Practice focus
Build fewestStamps first, then return exactly what the tasks ask for. Follow the order, keep repeated values when the rule says so, and check the empty case.