JavaScriptAlgorithms/Graphs/Kosaraju.js at master · bachdx2812/JavaScriptAlgorithms · GitHub

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/**

* Author: Adrito Mukherjee

* Kosaraju's Algorithm implementation in Javascript

* Kosaraju's Algorithm finds all the connected components in a Directed Acyclic Graph (DAG)

* It uses Stack data structure to store the Topological Sorted Order of vertices and also Graph data structure

* Wikipedia: https://en.wikipedia.org/wiki/Kosaraju%27s_algorithm

class Kosaraju {

constructor (graph) {

this.connections = {}

this.reverseConnections = {}

this.stronglyConnectedComponents = []

for (const [i, j] of graph) {

this.addEdge(i, j)

}

this.topoSort()

return this.kosaraju()

}

addNode (node) {

// Function to add a node to the graph (connection represented by set)

this.connections[node] = new Set()

this.reverseConnections[node] = new Set()

this.topoSorted = []

}

addEdge (node1, node2) {

// Function to add an edge (adds the node too if they are not present in the graph)

if (!(node1 in this.connections) || !(node1 in this.reverseConnections)) {

this.addNode(node1)

}

if (!(node2 in this.connections) || !(node2 in this.reverseConnections)) {

this.addNode(node2)

}

this.connections[node1].add(node2)

this.reverseConnections[node2].add(node1)

}

dfsTopoSort (node, visited) {

visited.add(node)

for (const child of this.connections[node]) {

if (!visited.has(child)) this.dfsTopoSort(child, visited)

}

this.topoSorted.push(node)

}

topoSort () {

// Function to perform topological sorting

const visited = new Set()

const nodes = Object.keys(this.connections).map((key) => Number(key))

for (const node of nodes) {

if (!visited.has(node)) this.dfsTopoSort(node, visited)

}

dfsKosaraju (node, visited) {

visited.add(node)

this.stronglyConnectedComponents[

this.stronglyConnectedComponents.length - 1

].push(node)

for (const child of this.reverseConnections[node]) {

if (!visited.has(child)) this.dfsKosaraju(child, visited)

}

kosaraju () {

// Function to perform Kosaraju Algorithm

const visited = new Set()

while (this.topoSorted.length > 0) {

const node = this.topoSorted.pop()

if (!visited.has(node)) {

this.stronglyConnectedComponents.push([])

this.dfsKosaraju(node, visited)

}

return this.stronglyConnectedComponents

}

function kosaraju (graph) {

const stronglyConnectedComponents = new Kosaraju(graph)

return stronglyConnectedComponents

}

export { kosaraju }

// kosaraju([

// [1, 2],

// [2, 3],

// [3, 1],

// [2, 4],

// [4, 5],

// [5, 6],

// [6, 4],

// ])

// [ [ 1, 3, 2 ], [ 4, 6, 5 ] ]

JavaScriptAlgorithms/Graphs/Kosaraju.js at master · bachdx2812/JavaScriptAlgorithms · GitHub

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