Undo drawer: First qualifying slip
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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
stack. Use a stack, which is a pile where you add and remove items only at the top. Readreadingsfrom left to right. A number of 0 or more adds that number to the top. A negative number tells you how many top items to remove: -3 means remove up to three items. Stop if the stack becomes empty.stackis the final stack, from bottom to top. - Read
stackfrom left to right. Find the first number that is at leastkand store that number, not its position, infirstMatch. - Complete
undoDrawerFirstQualifyingSlipso it returnsfirstMatch. Return it, do not print it.
Example
If readings is [9, 8, 8, -8, 7] and k is 5, then stack is [7] and undoDrawerFirstQualifyingSlip returns 7.
Rules
- If no number is at least
k, return -1. k(a whole number from 1 to 8) is the threshold in task 2: compare each number with it.
Test data
TEST DATA 1: readings is [14, 14, 10, -4, 0] and k is 6.
TEST DATA 2: readings is [9, 9, 9, -5] and k is 2.
Examples
Input: readings = [14,14,10,-4,0] k = 6 Output: -1
stack is [0]. Here k is 6. No number is at least 6, so return -1.
Input: readings = [9,9,9,-5] k = 2 Output: -1
stack is []. Here k is 2. No number is at least 2, so return -1.
Input: readings = [] k = 1 Output: -1
stack is []. Here k is 1. No number is at least 1, so return -1.
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 stack 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.