OCR J277 2.1 / AQA 8525 algorithms
Find a target in an unsorted list without using in or index().
← All GCSE Python lessonsLinear search checks one item after another until it finds the target or reaches the end. It works on unsorted data and has worst-case linear time relative to the list length. Trace which item is examined on each pass.
Watch out: Avoid reporting success just because the loop finishes. Track whether a match was actually found.
Read this worked example. Predict its output, run it in Python 3, and explain how variables change.
def linear_search(values, target):
for position in range(len(values)):
if values[position] == target:
return position
return -1
print(linear_search([9, 3, 6, 1], 6))Find a target in an unsorted list without using in or index(). 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 linear_search(values, target):
for position in range(len(values)):
if values[position] == target:
return position
return -1
numbers = [9, 3, 6, 1]
for target in [6, 7, 9]:
position = linear_search(numbers, target)
if position == -1:
print(target, "not found")
else:
print(target, "found at", position)The reference is one possible approach. Test your own program before comparing.
Question: Why must the loop check the entire list in the worst case?
If the target is absent or last, every item may need comparison.
Explain one test you used, one problem you solved and one improvement you would make.
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