Add detect cycle.

src/algorithms/graph/detect-cycle/detectUndirectedCycleUsingDisjointSet.js

@@ -0,0 +1,31 @@
+import DisjointSet from '../../../data-structures/disjoint-set/DisjointSet';
+
+/**
+ * Detect cycle in undirected graph using disjoint sets.
+ *
+ * @param {Graph} graph
+ */
+export default function detectUndirectedCycleUsingDisjointSet(graph) {
+  // Create initial singleton disjoint sets for each graph vertex.
+  /** @param {GraphVertex} graphVertex */
+  const keyExtractor = graphVertex => graphVertex.getKey();
+  const disjointSet = new DisjointSet(keyExtractor);
+  graph.getAllVertices().forEach(graphVertex => disjointSet.makeSet(graphVertex));
+
+  // Go trough all graph edges one by one and check if edge vertices are from the
+  // different sets. In this case joint those sets together. Do this until you find
+  // an edge where to edge vertices are already in one set. This means that current
+  // edge will create a cycle.
+  let cycleFound = false;
+  /** @param {GraphEdge} graphEdge */
+  graph.getAllEdges().forEach((graphEdge) => {
+    if (disjointSet.inSameSet(graphEdge.startVertex, graphEdge.endVertex)) {
+      // Cycle found.
+      cycleFound = true;
+    } else {
+      disjointSet.union(graphEdge.startVertex, graphEdge.endVertex);
+    }
+  });
+
+  return cycleFound;
+}