Fix interpolationSearch looping forever when the seek element is above part of the range - #2219
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…e part of the range If the seek element is missing and larger than the highest element of the current range, the interpolated middle index lands beyond rightIndex, so rightIndex = middleIndex - 1 never shrinks the range. Return -1 when the seek element exceeds the range maximum, and add tests. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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interpolationSearchnever returns for some inputs where the seek element is missing:Trace: the first pass interpolates index 11 (
26 > 24) and setsrightIndex = 10. On the next pass the range is[2 ... 22], butvalueDelta(22) is larger thanrangeDelta(20), so the interpolated index isfloor(22 * 10 / 20) = 11, which is beyondrightIndex.sortedArray[11]is still> 24, sorightIndex = 11 - 1 = 10again, and the loop repeats forever.The function already returns
-1when the seek element is below the range (valueDelta < 0). This adds the symmetric check for a seek element above the range maximum (seekElement > sortedArray[rightIndex]), which also guaranteesvalueDelta <= rangeDelta, so the interpolated index always stays inside[leftIndex, rightIndex]and every iteration shrinks the range.Found by differential fuzzing (comparing 25+ algorithms in
src/algorithmsagainst simple reference implementations on random inputs); the fuzzer stopped on this input because it never finished. I added tests for the hanging input and a few similar ones (missing elements between and above existing values);npx jest src/algorithms/searchandeslintpass.Written with AI assistance (Claude Code); I reproduced the hang, traced the cause above, and ran the tests and linter.