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fix(interpolation-search): avoid infinite loop when seek element exceeds range #2226

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fix(interpolation-search): avoid infinite loop when seek element exceeds range #2226

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7 changes: 7 additions & 0 deletions src/algorithms/search/interpolation-search/__test__/interpolationSearch.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -21,4 +21,11 @@ describe('interpolationSearch', () => {
expect(interpolationSearch([1, 2, 3, 700, 800, 1200, 1300, 1400, 19000], 800)).toBe(4);
expect(interpolationSearch([0, 10, 11, 12, 13, 14, 15], 10)).toBe(1);
});

it('should not loop forever when the seek element is above part of the range', () => {
// Regression test: without the fix this call hangs forever.
expect(interpolationSearch([2, 4, 8, 8, 10, 12, 18, 20, 20, 20, 22, 26, 26, 28], 24)).toBe(-1);
expect(interpolationSearch([1, 2, 4, 8, 16, 32, 64, 128], 48)).toBe(-1);
expect(interpolationSearch([1, 3, 5, 7, 9], 8)).toBe(-1);
});
});
8 changes: 8 additions & 0 deletions src/algorithms/search/interpolation-search/interpolationSearch.js
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,14 @@ export default function interpolationSearch(sortedArray, seekElement) {
return -1;
}

// If the seek element is higher than the highest element from the range
// then there is no seek element exists in array. This check also guarantees
// that valueDelta is not greater than rangeDelta, so the interpolated
// middleIndex always stays inside of [leftIndex, rightIndex] range.
if (seekElement > sortedArray[rightIndex]) {
return -1;
}

// If range delta is zero then subarray contains all the same numbers
// and thus there is nothing to search for unless this range is all
// consists of seek number.
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