feat(graph) dfs

Author: amejiarosario

lib/data-structures/graphs/graph.js

@@ -1,4 +1,6 @@
 const Node = require('./node');
+const Stack = require('../stacks/stack');
+const Queue = require('../queues/queue');
 
 /**
  * Graph that uses an adjacent list
@@ -49,6 +51,13 @@ class Graph {
     return this.nodes.delete(value);
   }
 
+  /**
+   * Create a connection between source node and target node.
+   * If the graph is undirected it will also create the conneciton from target to destination.
+   * If the nodes doesn't exist then it will create them on the fly
+   * @param {any} source
+   * @param {any} target
+   */
   addEdge(source, target) {
     const sourceNode = this.addVertex(source);
     const targetNode = this.addVertex(target);
@@ -62,6 +71,12 @@ class Graph {
     return [sourceNode, targetNode];
   }
 
+  /**
+   * Remove connection between source node and target.
+   * If the graph is undirected it will also remove the conneciton from target to destination.
+   * @param {any} source
+   * @param {any} target
+   */
   removeEdge(source, target) {
     const sourceNode = this.nodes.get(source);
     const targetNode = this.nodes.get(target);
@@ -76,6 +91,22 @@ class Graph {
 
     return [sourceNode, targetNode];
   }
+
+  *dfs(first) {
+    const visited = new Map();
+    const visitList = new Stack();
+
+    visitList.add(first);
+
+    while(!visitList.isEmpty()) {
+      const node = visitList.remove();
+      if(node && !visited.has(node)) {
+        yield node;
+        visited.set(node);
+        node.getAdjacents().forEach(adj => visitList.add(adj));
+      }
+    }
+  }
 }
 
 Graph.UNDIRECTED = Symbol('directed graph'); // one-way edges

lib/data-structures/graphs/graph.spec.js

@@ -55,6 +55,12 @@ describe('Graph', () => {
       expect(a.adjacents.map(n => n.value)).toEqual(['b']);
       expect(b.adjacents.map(n => n.value)).toEqual(['a']);
     });
+
+    it('should add falsy values', () => {
+      const [first, second] = graph.addEdge(0, false);
+      expect(first.value).toBe(0);
+      expect(second.value).toBe(false);
+    })
   });
 
   describe('#removeEdge', () => {
@@ -89,4 +95,29 @@ describe('Graph', () => {
       expect(d).toBe(undefined);
     });
   });
+
+  describe('#dfs', () => {
+    let first;
+
+    beforeEach(() => {
+      const [a] = graph.addEdge(0, 1);
+      first = a;
+      graph.addEdge(0, 4);
+      graph.addEdge(0, 5);
+
+      graph.addEdge(1, 3);
+      graph.addEdge(1, 4);
+
+      graph.addEdge(2, 1);
+
+      graph.addEdge(3, 2);
+      graph.addEdge(3, 4);
+    });
+
+    it('should visit nodes using depth-first search', () => {
+      const visitedOrder = Array.from(graph.dfs(first)).map(v => v.value);
+      // expect(visitedOrder).toEqual([0, 1, 3, 2, 4, 5]);
+      expect(visitedOrder).toEqual([0, 5, 4, 1, 3, 2]);
+    });
+  });
 });