From 0ca0f187564f0c81daeab84bbbfbdbaec983f89b Mon Sep 17 00:00:00 2001
From: xingzihai <xingzihai@users.noreply.github.com>
Date: Thu, 15 Oct 2026 07:19:23 +0000
Subject: [PATCH] fix(interpolation-search): avoid infinite loop when seek
 element exceeds range (fixes #2219)

interpolationSearch could loop forever when the seek element was greater
than sortedArray[rightIndex] while the range still contained values above
it: valueDelta could exceed rangeDelta, producing a middleIndex beyond
rightIndex, so rightIndex never changed and the loop repeated.

Add the symmetric early-return check (seekElement > sortedArray[rightIndex])
mirroring the existing valueDelta < 0 check. This also guarantees the
interpolated middleIndex stays inside [leftIndex, rightIndex], so every
iteration shrinks the search range.

Add regression tests for the reported input and similar cases.
---
 .../__test__/interpolationSearch.test.js                  | 7 +++++++
 .../search/interpolation-search/interpolationSearch.js    | 8 ++++++++
 2 files changed, 15 insertions(+)

diff --git a/src/algorithms/search/interpolation-search/__test__/interpolationSearch.test.js b/src/algorithms/search/interpolation-search/__test__/interpolationSearch.test.js
index 7ddc548b63..21d7576c7d 100644
--- a/src/algorithms/search/interpolation-search/__test__/interpolationSearch.test.js
+++ b/src/algorithms/search/interpolation-search/__test__/interpolationSearch.test.js
@@ -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);
+  });
 });
diff --git a/src/algorithms/search/interpolation-search/interpolationSearch.js b/src/algorithms/search/interpolation-search/interpolationSearch.js
index 8546c5be3b..11a51badea 100644
--- a/src/algorithms/search/interpolation-search/interpolationSearch.js
+++ b/src/algorithms/search/interpolation-search/interpolationSearch.js
@@ -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.