From 3e0ac7486c9eaa000f9900c84f929ccd0d91bab4 Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Tue, 22 May 2018 07:10:46 +0300
Subject: [PATCH] Use Infinity instead of zero in Graph adjacency matrix to
 show that vertices are not connected.

---
 .../graph/hamiltonian-cycle/hamiltonianCycle.js  |  4 ++--
 src/data-structures/graph/Graph.js               |  9 ++++-----
 src/data-structures/graph/__test__/Graph.test.js | 16 ++++++++--------
 3 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/src/algorithms/graph/hamiltonian-cycle/hamiltonianCycle.js b/src/algorithms/graph/hamiltonian-cycle/hamiltonianCycle.js
index 84562615..329821fe 100644
--- a/src/algorithms/graph/hamiltonian-cycle/hamiltonianCycle.js
+++ b/src/algorithms/graph/hamiltonian-cycle/hamiltonianCycle.js
@@ -15,7 +15,7 @@ function isSafe(adjacencyMatrix, verticesIndices, cycle, vertexCandidate) {
   const endVertexAdjacencyIndex = verticesIndices[endVertex.getKey()];
 
   // Check if last vertex in the path and candidate vertex are adjacent.
-  if (!adjacencyMatrix[endVertexAdjacencyIndex][candidateVertexAdjacencyIndex]) {
+  if (adjacencyMatrix[endVertexAdjacencyIndex][candidateVertexAdjacencyIndex] === Infinity) {
     return false;
   }
 
@@ -43,7 +43,7 @@ function isCycle(adjacencyMatrix, verticesIndices, cycle) {
   const endVertexAdjacencyIndex = verticesIndices[endVertex.getKey()];
 
   // Check if we can go from end vertex to the start one.
-  return !!adjacencyMatrix[endVertexAdjacencyIndex][startVertexAdjacencyIndex];
+  return adjacencyMatrix[endVertexAdjacencyIndex][startVertexAdjacencyIndex] !== Infinity;
 }
 
 /**
diff --git a/src/data-structures/graph/Graph.js b/src/data-structures/graph/Graph.js
index b3ee8730..d9ac9089 100644
--- a/src/data-structures/graph/Graph.js
+++ b/src/data-structures/graph/Graph.js
@@ -177,18 +177,17 @@ export default class Graph {
     const vertices = this.getAllVertices();
     const verticesIndices = this.getVerticesIndices();
 
-    // Init matrix with zeros.
+    // Init matrix with infinities meaning that there is no ways of
+    // getting from one vertex to another yet.
     const adjacencyMatrix = Array(vertices.length).fill(null).map(() => {
-      return Array(vertices.length).fill(0);
+      return Array(vertices.length).fill(Infinity);
     });
 
     // Fill the columns.
     vertices.forEach((vertex, vertexIndex) => {
       vertex.getNeighbors().forEach((neighbor) => {
         const neighborIndex = verticesIndices[neighbor.getKey()];
-        adjacencyMatrix[vertexIndex][neighborIndex] = this.isDirected ?
-          this.findEdge(vertex, neighbor).weight :
-          1;
+        adjacencyMatrix[vertexIndex][neighborIndex] = this.findEdge(vertex, neighbor).weight;
       });
     });
 
diff --git a/src/data-structures/graph/__test__/Graph.test.js b/src/data-structures/graph/__test__/Graph.test.js
index e89093b8..1c6592ba 100644
--- a/src/data-structures/graph/__test__/Graph.test.js
+++ b/src/data-structures/graph/__test__/Graph.test.js
@@ -348,10 +348,10 @@ describe('Graph', () => {
 
     const adjacencyMatrix = graph.getAdjacencyMatrix();
     expect(adjacencyMatrix).toEqual([
-      [0, 1, 0, 0],
-      [1, 0, 1, 1],
-      [0, 1, 0, 1],
-      [0, 1, 1, 0],
+      [Infinity, 0, Infinity, Infinity],
+      [0, Infinity, 0, 0],
+      [Infinity, 0, Infinity, 0],
+      [Infinity, 0, 0, Infinity],
     ]);
   });
 
@@ -375,10 +375,10 @@ describe('Graph', () => {
 
     const adjacencyMatrix = graph.getAdjacencyMatrix();
     expect(adjacencyMatrix).toEqual([
-      [0, 2, 0, 0],
-      [0, 0, 1, 7],
-      [0, 0, 0, 5],
-      [0, 0, 0, 0],
+      [Infinity, 2, Infinity, Infinity],
+      [Infinity, Infinity, 1, 7],
+      [Infinity, Infinity, Infinity, 5],
+      [Infinity, Infinity, Infinity, Infinity],
     ]);
   });
 });