Summary
In quickSortSteps.js, the swap step inside performPartition reads arr[j] after the destructuring swap mutates the array. The message shows the old arr[i] value (already placed from a previous iteration) instead of the current element that was actually smaller than the pivot.
Steps to reproduce
- Open AlgoScope and navigate to Quick Sort.
- Generate an array and start the visualization.
- Watch the swap step messages during partitioning — the value highlighted as "smaller than pivot" is incorrect when
i !== j.
Expected behavior
The message should show the element that was detected as smaller than the pivot and is being moved to the left partition.
Actual behavior
Because the destructuring swap [arr[i], arr[j]] = [arr[j], arr[i]] executes before the message template reads arr[j], the message reads the replaced value at index j (the old arr[i] from a previous pass) instead of the current element being moved.
// Current code (broken — swap before message)
[arr[i], arr[j]] = [arr[j], arr[i]]
steps.push(createStep({
message: `${arr[j]} is smaller than pivot, move it to index ${i}.`, // arr[j] is now old arr[i]!
...
}))Fix
Capture the pre-swap value before the destructuring:
const smallerValue = arr[j]
;[arr[i], arr[j]] = [arr[j], arr[i]]
steps.push(createStep({
message: `${smallerValue} is smaller than pivot, move it to index ${i}.`,
...
}))File
src/algorithms/sorting/quickSortSteps.js — inside performPartition(), around line 135.
Operating system
Any
AlgoScope version
1.13.0
Summary
In
quickSortSteps.js, the swap step insideperformPartitionreadsarr[j]after the destructuring swap mutates the array. The message shows the oldarr[i]value (already placed from a previous iteration) instead of the current element that was actually smaller than the pivot.Steps to reproduce
i !== j.Expected behavior
The message should show the element that was detected as smaller than the pivot and is being moved to the left partition.
Actual behavior
Because the destructuring swap
[arr[i], arr[j]] = [arr[j], arr[i]]executes before the message template readsarr[j], the message reads the replaced value at indexj(the oldarr[i]from a previous pass) instead of the current element being moved.Fix
Capture the pre-swap value before the destructuring:
File
src/algorithms/sorting/quickSortSteps.js— insideperformPartition(), around line 135.Operating system
Any
AlgoScope version
1.13.0