Canceling stamps: Even-key census
Stuck or curious how this works? Visualize Stack Operations ↗
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
remaining. Treatreadingsas a row of stamps. Keep a stack, which is a pile where you can add or remove only the top stamp. Read the stamps from left to right. If the next stamp matches the top stamp, remove the top stamp and do not add the new one. Otherwise, put the new stamp on top.remainingis the final stack, from bottom to top. - Count the even numbers in
remaining. Store the count inevenCount. A number is even when it divides by 2 with no remainder. - Complete
cancelingStampsEvenKeyCensusso it returnsevenCount. Return it, do not print it.
Example
If readings is [3, 3, 8, -1, 7], then remaining is [8, -1, 7] and cancelingStampsEvenKeyCensus returns 1.
Rules
- 0 and negative even numbers count too.
- If
remainingis empty, return 0.
Test data
TEST DATA 1: readings is [-7, 0, 8, 5, 5].
TEST DATA 2: readings is [3, -2, 3, 3].
Examples
Input: readings = [-7,0,8,5,5] Output: 2
remaining is [-7, 0, 8]. The even numbers are [0, 8]. There are 2, so return 2.
Input: readings = [3,-2,3,3] Output: 1
remaining is [3, -2]. The even numbers are [-2]. There are 1, so return 1.
Input: readings = [] Output: 0
remaining 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 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 remaining 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.