Prefix stencils: Even-key census
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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
rangeSums. For each position inreadings, add the current number and up tok- 1 numbers just before it. Stop at the start of the input if needed. Record each sum, from left to right. Forreadings= [2, 3, 4] andk= 2,rangeSumsis [2, 5, 7]. - Count the even numbers in
rangeSums. Store the count inevenCount. A number is even when it divides by 2 with no remainder. - Complete
prefixStencilsEvenKeyCensusso it returnsevenCount. Return it, do not print it.
Example
If readings is [8, 5, 5, 3, -7] and k is 5, then rangeSums is [8, 13, 18, 21, 14] and prefixStencilsEvenKeyCensus returns 3.
Rules
- 0 and negative even numbers count too.
- If
rangeSumsis empty, return 0. k(a whole number from 1 to 8) is the most numbers each sum in task 1 may include.
Test data
TEST DATA 1: readings is [17, 17, -8, 14, 0] and k is 1.
TEST DATA 2: readings is [4, -6, 4, 4] and k is 2.
Examples
Input: readings = [17,17,-8,14,0] k = 1 Output: 3
rangeSums is [17, 17, -8, 14, 0]. The even numbers are [-8, 14, 0]. There are 3, so return 3.
Input: readings = [4,-6,4,4] k = 2 Output: 4
rangeSums is [4, -2, -2, 8]. The even numbers are [4, -2, -2, 8]. There are 4, so return 4.
Input: readings = [] k = 3 Output: 0
rangeSums is []. The even numbers are []. There are 0, so return 0.
Input limits
- 0 <= input size <= 64.
- k is a whole number from 1 to 8. Answers fit in a signed 32-bit integer: -2,147,483,648 through 2,147,483,647.
- Input numbers have no decimal part. They range from -1,000,000 to 1,000,000. Follow any extra input rules in task 1.
Efficiency goal
Big-O describes how the work or memory needed grows as the input gets larger.
Efficiency goal: time O(n); extra memory, including the helper list, O(n). n is the input length. These labels describe how work and memory grow with the input.
Practice focus
Build rangeSums 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.