chore: Added BellmanFord (#679)

Mayank17M · web-flow · commit d49cf9feadfa · 2021-09-09T16:46:52.000+05:30
* Added BellmanFord

* Add References for BellmanFord

* Style code using standard.js

* Add tests and modify code

* Fixed BellmanFord test file

* Add BellmanFord and tests
diff --git a/Graphs/BellmanFord.js b/Graphs/BellmanFord.js
@@ -0,0 +1,56 @@
+/*
+The Bellman–Ford algorithm is an algorithm that computes shortest paths
+from a single source vertex to all of the other vertices in a weighted digraph.
+It also detects negative weight cycle.
+
+Complexity:
+    Worst-case performance O(VE)
+    Best-case performance O(E)
+    Worst-case space complexity O(V)
+
+Reference:
+    https://en.wikipedia.org/wiki/Bellman–Ford_algorithm
+    https://cp-algorithms.com/graph/bellman_ford.html
+
+*/
+
+/**
+ *
+ * @param graph Graph in the format (u, v, w) where
+ *  the edge is from vertex u to v. And weight
+ *  of the edge is w.
+ * @param V Number of vertices in graph
+ * @param E Number of edges in graph
+ * @param src Starting node
+ * @param dest Destination node
+ * @returns Shortest distance from source to destination
+ */
+function BellmanFord (graph, V, E, src, dest) {
+  // Initialize distance of all vertices as infinite.
+  const dis = Array(V).fill(Infinity)
+  // initialize distance of source as 0
+  dis[src] = 0
+
+  // Relax all edges |V| - 1 times. A simple
+  // shortest path from src to any other
+  // vertex can have at-most |V| - 1 edges
+  for (let i = 0; i < V - 1; i++) {
+    for (let j = 0; j < E; j++) {
+      if ((dis[graph[j][0]] + graph[j][2]) < dis[graph[j][1]]) { dis[graph[j][1]] = dis[graph[j][0]] + graph[j][2] }
+    }
+  }
+  // check for negative-weight cycles.
+  for (let i = 0; i < E; i++) {
+    const x = graph[i][0]
+    const y = graph[i][1]
+    const weight = graph[i][2]
+    if ((dis[x] !== Infinity) && (dis[x] + weight < dis[y])) {
+      return null
+    }
+  }
+  for (let i = 0; i < V; i++) {
+    if (i === dest) return dis[i]
+  }
+}
+
+export { BellmanFord }
diff --git a/Graphs/test/BellmanFord.test.js b/Graphs/test/BellmanFord.test.js
@@ -0,0 +1,34 @@
+import { BellmanFord } from '../BellmanFord.js'
+
+test('Test Case 1', () => {
+  const V = 5
+  const E = 8
+  const destination = 3
+  const graph = [[0, 1, -1], [0, 2, 4],
+    [1, 2, 3], [1, 3, 2],
+    [1, 4, 2], [3, 2, 5],
+    [3, 1, 1], [4, 3, -3]]
+  const dist = BellmanFord(graph, V, E, 0, destination)
+  expect(dist).toBe(-2)
+})
+test('Test Case 2', () => {
+  const V = 6
+  const E = 9
+  const destination = 4
+  const graph = [[0, 1, 3], [0, 3, 6],
+    [0, 5, -1], [1, 2, -3],
+    [1, 4, -2], [5, 2, 5],
+    [2, 3, 1], [4, 3, 5], [5, 4, 2]]
+  const dist = BellmanFord(graph, V, E, 0, destination)
+  expect(dist).toBe(1)
+})
+test('Test Case 3', () => {
+  const V = 4
+  const E = 5
+  const destination = 1
+  const graph = [[0, 3, -1], [0, 2, 4],
+    [3, 2, 2], [3, 1, 5],
+    [2, 1, -1]]
+  const dist = BellmanFord(graph, V, E, 0, destination)
+  expect(dist).toBe(0)
+})
