OCR J277 2.1 / AQA 8525 algorithms
Swap adjacent out-of-order items and record the result of each pass.
← All GCSE Python lessonsBubble sort compares neighbouring values, swapping those that are out of order. After each full pass the largest remaining item moves towards its final position. Record the list after each comparison to see how the algorithm progresses.
Watch out: Do not use Python sort() in an exercise that asks you to implement the algorithm yourself.
Read this worked example. Predict its output, run it in Python 3, and explain how variables change.
values = [5, 2, 4, 1]
for end in range(len(values)-1, 0, -1):
for i in range(end):
if values[i] > values[i+1]:
values[i], values[i+1] = values[i+1], values[i]
print(values)Swap adjacent out-of-order items and record the result of each pass. Work from the starter code before comparing with the solution.
Download starter + solution ZIP ↓For a stretch challenge: add meaningful test data, handle an edge case and explain one design decision.
def bubble_sort(values):
data = values.copy()
for end in range(len(data)-1, 0, -1):
swapped = False
for i in range(end):
if data[i] > data[i+1]:
data[i], data[i+1] = data[i+1], data[i]
swapped = True
if not swapped:
break
return data
for data in ([5,2,4,1], [1,2,3], []):
print(data, '->', bubble_sort(data))The reference is one possible approach. Test your own program before comparing.
Question: Why is the inner loop bound reduced after each pass?
After each complete pass, the largest remaining value is in its final position.
Explain one test you used, one problem you solved and one improvement you would make.
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