Shift and append bits
Mirror an Eight-Switch Panel
01. The question
Reverse all eight positions of an unsigned byte and return the resulting integer. Variant: exactly 8 bits, not 32; leading zeros are real positions and must be reversed too.
Before revealing the idea, predict the result and describe what information you would need to track.
02. Worked example
Input22
Output104
- Write 22 as 00010110, including its leading zeros.
- Read one low bit at a time and append it to the growing result.
- After exactly eight steps the result is 01101000, or 104.
Try your code
Define solve(data, parameter="") and return your result. Your code runs locally, not on a server.
Edit your test cases
Use 1-10 objects with data and an optional string parameter. Expected outputs are computed from the lesson. An optional expected field must be correct.
Input contract & reference code
Example data: 22. Parameter: "". Numeric parameters arrive as strings; convert them with int(parameter) when needed.
The example and generated cases use the question’s exact variant. This checks behavior on a small test batch—not performance on every possible input.
Python downloads only when you run code, using compressed runtime assets. Code is not saved or uploaded. Enable JavaScript to run it.
Printed output
Five-second execution limit per batch. Standard-library Python only; additional packages and network access are unavailable. Stop ends execution without blocking the lesson.
03. The idea
Try sketching your own approach first. What would you track, and why would it work?
Reveal the idea
- Shift the result left before appending the next low input bit.
- Shift remaining input right.
- Always take eight steps, even after remaining becomes zero.
04. Watch it happen
Use Step to move slowly, or Play to follow the whole trace. Change a preset or load your own input.
Input & settings
Red = current item / blue = active window or cells / green = completed work. A value docks at its actual destination; the original input stays unchanged. Positions start at 0.
Working state / what changes
Ready to begin
Enable JavaScript to step through the animation. The worked example and solution below remain readable without it.
Python / why it changes
The line behind the step
def solve(data, parameter=''):
remaining = data
reversed_byte = 0
for step in range(8):
reversed_byte = (reversed_byte << 1) | (remaining & 1)
remaining >>= 1
return reversed_byteHow to use this walkthrough
Hover or focus a control for its label. Play forms the input and follows values into the working state. Step shows one change; Back and the slider restore exact snapshots. Reduced motion uses instant updates. Saved snapshots and sorted heap displays are teaching overhead, not algorithm complexity.
05. Python solution
def solve(data, parameter=''):
remaining = data
reversed_byte = 0
for step in range(8):
reversed_byte = (reversed_byte << 1) | (remaining & 1)
remaining >>= 1
return reversed_byte06. Cost & edge cases
- Time
- O(w), w = 8
- Space
- O(1)
- 0 mirrors to 0 and 255 mirrors to 255.
- 1 mirrors to 128, not to 1.
- Require a JSON integer from 0 to 255.