From 0b34d7d963f67699d34ed9df714fbabb4e986400 Mon Sep 17 00:00:00 2001
From: Gonzalo Blasco <gonzoblasco@gmail.com>
Date: Wed, 5 Aug 2026 05:37:48 -0300
Subject: [PATCH] fix(#2057): return ordered cycle path array instead of parent
 mapping in detectUndirectedCycle

The function was returning an object mapping vertex keys to their parent
vertices, which is not a standard cycle representation. Changed to return
an ordered array of vertices forming the cycle, starting and ending at
the same vertex.

Fixes #2057
---
 .../__test__/detectUndirectedCycle.test.js          | 13 +++++++------
 .../graph/detect-cycle/detectUndirectedCycle.js     | 12 ++++++------
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/src/algorithms/graph/detect-cycle/__test__/detectUndirectedCycle.test.js b/src/algorithms/graph/detect-cycle/__test__/detectUndirectedCycle.test.js
index c3f9903102..76c0778c14 100644
--- a/src/algorithms/graph/detect-cycle/__test__/detectUndirectedCycle.test.js
+++ b/src/algorithms/graph/detect-cycle/__test__/detectUndirectedCycle.test.js
@@ -31,11 +31,12 @@ describe('detectUndirectedCycle', () => {
 
     graph.addEdge(edgeDE);
 
-    expect(detectUndirectedCycle(graph)).toEqual({
-      B: vertexC,
-      C: vertexD,
-      D: vertexE,
-      E: vertexB,
-    });
+    expect(detectUndirectedCycle(graph)).toEqual([
+      vertexB,
+      vertexC,
+      vertexD,
+      vertexE,
+      vertexB,
+    ]);
   });
 });
diff --git a/src/algorithms/graph/detect-cycle/detectUndirectedCycle.js b/src/algorithms/graph/detect-cycle/detectUndirectedCycle.js
index 5bcc9bb699..bfac742a1c 100644
--- a/src/algorithms/graph/detect-cycle/detectUndirectedCycle.js
+++ b/src/algorithms/graph/detect-cycle/detectUndirectedCycle.js
@@ -30,19 +30,19 @@ export default function detectUndirectedCycle(graph) {
     },
     enterVertex: ({ currentVertex, previousVertex }) => {
       if (visitedVertices[currentVertex.getKey()]) {
-        // Compile cycle path based on parents of previous vertices.
-        cycle = {};
+        // Build an ordered cycle path array starting and ending at the repeated vertex.
+        const cyclePath = [currentVertex];
 
-        let currentCycleVertex = currentVertex;
         let previousCycleVertex = previousVertex;
 
         while (previousCycleVertex.getKey() !== currentVertex.getKey()) {
-          cycle[currentCycleVertex.getKey()] = previousCycleVertex;
-          currentCycleVertex = previousCycleVertex;
+          cyclePath.push(previousCycleVertex);
           previousCycleVertex = parents[previousCycleVertex.getKey()];
         }
 
-        cycle[currentCycleVertex.getKey()] = previousCycleVertex;
+        cyclePath.push(previousCycleVertex);
+
+        cycle = cyclePath;
       } else {
         // Add next vertex to visited set.
         visitedVertices[currentVertex.getKey()] = currentVertex;