Index-tracked open-set heap: O(log n) decrease-key + sift-down fix#7
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GenerelSchwerz merged 1 commit intoJun 18, 2026
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…x sift-down The A* open set is a binary min-heap. It had two issues: 1. Correctness: pop()'s sift-down used `smallerChild < size - 1`, which skips the right child when it is the final slot. pop() could therefore leave the minimum off the root, so A* popped nodes out of f-order -- exploring extra nodes and able to return a worse path. 2. Performance: update() (decrease-key, called whenever A* finds a cheaper route to an already-open node) did `heap.indexOf(val)` -- an O(n) scan over the whole open set, i.e. ~O(n^2) across a search. Fix: each node stores its slot in `heapIdx`, maintained on every sift, so update() is O(log n) with no scan. Sift-up/down are rewritten with the correct child bound; pop() uses Array.pop() instead of splice. Tests: tests/heap.test.ts (ascending order, the boundary regression, decrease-key, heapIdx lifecycle, 200-node randomized stress). All existing pathfinder tests still pass, so real A* output is unchanged -- just correct and faster.
GenerelSchwerz
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Minecraft-Pathfinding:2026-rewrite
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Open-set heap: fix sift-down + O(log n) decrease-key
A* uses a binary min-heap (
src/abstract/heap.ts) as its open set. Two issues:1. Correctness bug in
pop()— the sift-down's right-child guard wassmallerChild < size - 1, off by one: when the smaller child is the last slot it gets skipped, sopop()can leave the minimum off the root. A* then pops nodes out offorder — exploring extra nodes and able to return a worse path.2.
update()was O(n) — decrease-key (called whenever A* finds a cheaper route to an already-open node) didheap.indexOf(val), a linear scan over the whole open set → ~O(n²) across a search.Fix
Every node now stores its slot in
heapIdx, maintained on each sift, soupdate()is O(log n) with no scan. Sift-up/down are rewritten with the correct child bound;pop()usesArray.pop()instead ofsplice.Tests
tests/heap.test.ts:forder,[1, 8, …]instead of[1, 2, …]),update()decrease-key,heapIdxlifecycle (set on push,-1after pop),All existing pathfinder tests still pass, so real A* output is unchanged — just correct and faster.
tscbuild clean,ts-standardreports 0 problems.