Fix 0/1 Knapsack traceback crash and incorrect item selection#2109
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danielalanbates wants to merge 1 commit intotrekhleb:masterfrom
Open
Fix 0/1 Knapsack traceback crash and incorrect item selection#2109danielalanbates wants to merge 1 commit intotrekhleb:masterfrom
danielalanbates wants to merge 1 commit intotrekhleb:masterfrom
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The traceback phase of solveZeroOneKnapsackProblem() had two bugs: 1. Accessed knapsackMatrix[itemIndex - 2] without bounds checking, causing "Cannot read property of undefined" when itemIndex was 1. 2. Used incorrect logic that pushed prevItem instead of currentItem when an item was included, leading to wrong selected items. Replaced with the standard DP traceback: if dp[i][w] != dp[i-1][w], item i was included. Also added check for the first item (row 0). Added test case from issue trekhleb#248 that previously crashed. Fixes trekhleb#248
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Summary
Fixes two bugs in
solveZeroOneKnapsackProblem()traceback phase:Crash:
knapsackMatrix[itemIndex - 2][weightIndex]accessed out-of-bounds whenitemIndex === 1, causingTypeError: Cannot read property of undefined.Wrong items selected: The traceback pushed
prevIteminstead ofcurrentItemwhen including an item, producing incorrect results even when the crash didn't occur.Changes
Replaced the buggy traceback logic with the standard 0/1 knapsack DP traceback:
dp[i][w] !== dp[i-1][w], itemiwas included — push it and reduce weight.Added a test case using the exact input from #248 that previously crashed.
Testing
All 8 tests pass (7 existing + 1 new):
should solve 0/1 knapsack problemshould solve 0/1 knapsack problem regardless of items ordershould solve 0/1 knapsack problem with no single-weight-1 item (issue #248)[NEW]should solve 0/1 knapsack problem with impossible items setshould solve 0/1 knapsack problem with all equal weightsFixes #248
This PR was created with AI assistance to help this open-source project. Happy to make any adjustments!