Patch buildComponent in eles.htbc()

- For certain graph structures, it is possible for a single edge (or multiple, counting loops) to be omitted from a component during it's construction. This ensures that components are reconstructed in their entirety.
- Add test case which fails without newest modification
- Additional clean up
- Rename `eles.hopcroftTarjan()` to `eles.htbc()` in documentation

Ref :  #2622

documentation/md/collection/hopcroftTarjanBiconnected.md

@@ -14,7 +14,7 @@ This function returns an object of the following form:
 ## Examples
 
 ```js
-var ht = cy.elements().hopcroftTarjan();
+var ht = cy.elements().htbc();
 
 ht.components[0].select();
 ```

src/collection/algorithms/hopcroft-tarjan-biconnected.js

@@ -1,19 +1,16 @@
 let hopcroftTarjanBiconnected = function() {
-
   let eles = this;
   let nodes = {};
   let id = 0;
   let edgeCount = 0;
   let components = [];
   let stack = [];
   let visitedEdges = {};
-  let loops = {};
 
   const buildComponent = (x, y) => {
     let i = stack.length-1;
     let cutset = [];
-    let visitedNodes = {};
-    let component = [];
+    let component = eles.spawn();
 
     while (stack[i].x != x || stack[i].y != y) {
       cutset.push(stack.pop().edge);
@@ -22,88 +19,82 @@ let hopcroftTarjanBiconnected = function() {
     cutset.push(stack.pop().edge);
 
     cutset.forEach(edge => {
-      component.push(edge);
-      let connectedNodes = edge.connectedNodes().intersection(eles);
-
+      let connectedNodes = edge.connectedNodes()
+                               .intersection(eles);
+      component.merge(edge);
       connectedNodes.forEach(node => {
-        let nodeId = node.id();
-
-        if (!(nodeId in visitedNodes)) {
-          visitedNodes[nodeId] = true;
-
-          if (nodeId in loops) {
-            loops[nodeId].forEach(loop => component.push(loop));
-          }
-          component.push(node);
+        const nodeId = node.id();
+        const connectedEdges = node.connectedEdges()
+                                   .intersection(eles);
+        component.merge(node);
+        if (!nodes[nodeId].cutVertex) {
+          component.merge(connectedEdges);
+        } else {
+          component.merge(connectedEdges.filter(edge => edge.isLoop()));
         }
       });
     });
-
-    components.push(eles.spawn(component));
+    components.push(component);
   };
 
   const biconnectedSearch = (root, currentNode, parent) => {
-    if (root == parent) edgeCount += 1;
+    if (root === parent) edgeCount += 1;
     nodes[currentNode] = {
       id : id,
       low : id++,
       cutVertex : false
     };
-    let edges = eles.getElementById(currentNode).connectedEdges().intersection(eles);
+    let edges = eles.getElementById(currentNode)
+                    .connectedEdges()
+                    .intersection(eles);
 
     if (edges.size() === 0) {
       components.push(eles.spawn(eles.getElementById(currentNode)));
     } else {
-      let sourceId, targetId, otherNodeId, edgeId, isEdgeLoop;
+      let sourceId, targetId, otherNodeId, edgeId;
 
       edges.forEach(edge => {
         sourceId = edge.source().id();
         targetId = edge.target().id();
-        otherNodeId = (sourceId == currentNode) ? targetId : sourceId;
-        isEdgeLoop = edge.isLoop();
+        otherNodeId = (sourceId === currentNode) ? targetId : sourceId;
 
-        if (isEdgeLoop) {
-          if (sourceId in loops) {
-            loops.push(edge);
-          } else {
-            loops[sourceId] = [edge];
-          }
-        } else if (otherNodeId != parent) {
+        if (otherNodeId !== parent) {
           edgeId = edge.id();
 
           if (!visitedEdges[edgeId]) {
             visitedEdges[edgeId] = true;
             stack.push({
               x : currentNode,
               y : otherNodeId,
-              edge : eles.getElementById(edgeId)
+              edge
             });
           }
 
           if (!(otherNodeId in nodes)) {
             biconnectedSearch(root, otherNodeId, currentNode);
-            nodes[currentNode].low = Math.min(nodes[currentNode].low, nodes[otherNodeId].low);
+            nodes[currentNode].low = Math.min(nodes[currentNode].low,
+                                              nodes[otherNodeId].low);
 
             if (nodes[currentNode].id <= nodes[otherNodeId].low) {
               nodes[currentNode].cutVertex = true;
               buildComponent(currentNode, otherNodeId);
             }
           } else {
-            nodes[currentNode].low = Math.min(nodes[currentNode].low, nodes[otherNodeId].id);
+            nodes[currentNode].low = Math.min(nodes[currentNode].low,
+                                              nodes[otherNodeId].id);
           }
         }
       });
     }
   };
 
   eles.forEach(ele => {
-
     if (ele.isNode()) {
       let nodeId = ele.id();
 
       if (!(nodeId in nodes)) {
         edgeCount = 0;
-        biconnectedSearch(nodeId, nodeId, "");
+        biconnectedSearch(nodeId, nodeId);
         nodes[nodeId].cutVertex = (edgeCount > 1);
       }
     }
@@ -115,14 +106,13 @@ let hopcroftTarjanBiconnected = function() {
 
   return {
     cut: eles.spawn(cutVertices),
-    components: components
+    components
   };
-
 };
 
-export default { 
-  hopcroftTarjanBiconnected, 
-  htbc: hopcroftTarjanBiconnected, 
+export default {
+  hopcroftTarjanBiconnected,
+  htbc: hopcroftTarjanBiconnected,
   htb: hopcroftTarjanBiconnected,
   hopcroftTarjanBiconnectedComponents: hopcroftTarjanBiconnected
 };

test/collection-hopcroft-tarjan-biconnected.js

@@ -4,7 +4,7 @@ var cytoscape = require('../src/test.js', cytoscape);
 describe('Algorithms', function(){
   describe('eles.hopcroftTarjanBiconnected()', function(){
 
-    var cy0, cy1;
+    var cy0, cy1, cy2;
 
     beforeEach(function(done) {
       cytoscape({
@@ -34,7 +34,11 @@ describe('Algorithms', function(){
             { data: { id: '1-15' } },
             { data: { id: '1-16' } },
             { data: { id: '1-17' } },
-            { data: { id: '1-18' } }
+            { data: { id: '1-18' } },
+
+            { data: { id: '2-0' } },
+            { data: { id: '2-1' } },
+            { data: { id: '2-2' } },
           ],
 
           edges: [
@@ -71,13 +75,21 @@ describe('Algorithms', function(){
             { data: { source: '1-12', target: '1-13', id: '1-41' } },
             { data: { source: '1-13', target: '1-14', id: '1-42' } },
             { data: { source: '1-13', target: '1-15', id: '1-43' } },
-            { data: { source: '1-17', target: '1-18', id: '1-44' } }
+            { data: { source: '1-17', target: '1-18', id: '1-44' } },
+
+            { data: { id: '2-3', source: '2-2', target: '2-1' } },
+            { data: { id: '2-4', source: '2-1', target: '2-0' } },
+            { data: { id: '2-5', source: '2-1', target: '2-1' } },
+            { data: { id: '2-6', source: '2-0', target: '2-1' } },
+            { data: { id: '2-7', source: '2-0', target: '2-2' } },
+            { data: { id: '2-8', source: '2-0', target: '2-0' } }
           ]
         },
 
         ready: function(){
           cy0 = this.filter(ele => ele.id()[0] == "0");
           cy1 = this.filter(ele => ele.id()[0] == "1");
+          cy2 = this.filter(ele => ele.id()[0] == "2");
           done();
         }
       });
@@ -88,10 +100,18 @@ describe('Algorithms', function(){
     }
 
     it('eles.htbc(): no cut vertices, one biconnected component', function(){
-      var res = cy0.htbc();
-      expect( res.cut.map( ele2id ) ).to.deep.equal( [] );
-      expect( res.components.length ).to.equal( 1 );
-      expect( res.components[0].map( ele2id ) ).to.deep.equal( [ "0-9", "0-11", "0-4", "0-3", "0-10", "0-0", "0-8", "0-7", "0-2", "0-6", "0-1", "0-5" ] );
+      var res0 = cy0.htbc();
+      var res1 = cy2.htbc();
+      expect( res0.cut.map( ele2id ) ).to.deep.equal( [] );
+      expect( res0.components.length ).to.equal( 1 );
+      expect( res0.components[0].length ).to.equal( cy0.length );
+      expect( res0.components[0].map( ele2id ) ).to.deep.equal( [ "0-9", "0-4", "0-8", "0-10", "0-11", "0-3", "0-7", "0-0", "0-2", "0-6", "0-1", "0-5"] );
+
+      expect( res1.cut.map( ele2id ) ).to.deep.equal( [] );
+      expect( res1.components.length ).to.equal( 1 );
+      expect( res1.components[0].length ).to.equal( cy2.length );
+      expect( res1.components[0].map( ele2id ) ).to.deep.equal( [ "2-5", "2-1", "2-3", "2-4", "2-6", "2-7", "2-0", "2-8", "2-2" ] );
+
     });
 
     it('eles.htbc(): multiple biconnected components', function(){
@@ -102,9 +122,9 @@ describe('Algorithms', function(){
       expect( res.components[1].map( ele2id ) ).to.deep.equal( [ "1-21", "1-2", "1-4", "1-24", "1-3", "1-20" ] );
       expect( res.components[2].map( ele2id ) ).to.deep.equal( [ "1-38", "1-10", "1-16" ] );
       expect( res.components[3].map( ele2id ) ).to.deep.equal( [ "1-40", "1-10", "1-18", "1-44", "1-17", "1-39" ] );
-      expect( res.components[4].map( ele2id ) ).to.deep.equal( [ "1-34", "1-8", "1-15", "1-43", "1-13", "1-33", "1-14", "1-42", "1-41", "1-12", "1-32" ] );
-      expect( res.components[5].map( ele2id ) ).to.deep.equal( [ "1-36", "1-9", "1-11", "1-31", "1-8", "1-29", "1-7", "1-37", "1-10", "1-35", "1-30", "1-28" ] );
-      expect( res.components[6].map( ele2id ) ).to.deep.equal( [ "1-26", "1-5", "1-7", "1-27", "1-6", "1-23", "1-2", "1-25", "1-22" ] );
+      expect( res.components[4].map( ele2id ) ).to.deep.equal( [ "1-34", "1-8", "1-15", "1-43", "1-13", "1-41", "1-42", "1-33", "1-14", "1-12", "1-32" ] );
+      expect( res.components[5].map( ele2id ) ).to.deep.equal( [ "1-36", "1-9", "1-30", "1-35", "1-11", "1-29", "1-31", "1-37", "1-8", "1-7", "1-10", "1-28" ] );
+      expect( res.components[6].map( ele2id ) ).to.deep.equal( [ "1-26", "1-5", "1-22", "1-25", "1-7", "1-27", "1-6", "1-23", "1-2"] );
       expect( res.components[7].map( ele2id ) ).to.deep.equal( [ "1-19", "1-1", "1-2" ] );
     });