package com.thealgorithms.graph;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Stack;
public class StronglyConnectedComponentOptimized {
public void btrack(HashMap<Integer, List<Integer>> adjList, int[] visited, Stack<Integer> dfsCallsNodes, int currentNode) {
visited[currentNode] = 1;
List<Integer> neighbors = adjList.get(currentNode);
if (neighbors != null) {
for (int neighbor : neighbors) {
if (visited[neighbor] == -1) {
btrack(adjList, visited, dfsCallsNodes, neighbor);
}
}
}
dfsCallsNodes.add(currentNode);
}
public void btrack2(HashMap<Integer, List<Integer>> adjRevList, int[] visited, int currentNode, List<Integer> newScc) {
visited[currentNode] = 1;
newScc.add(currentNode);
List<Integer> neighbors = adjRevList.get(currentNode);
if (neighbors != null) {
for (int neighbor : neighbors) {
if (visited[neighbor] == -1) {
btrack2(adjRevList, visited, neighbor, newScc);
}
}
}
}
public int getOutput(HashMap<Integer, List<Integer>> adjList, int n) {
int[] visited = new int[n];
Arrays.fill(visited, -1);
Stack<Integer> dfsCallsNodes = new Stack<>();
for (int i = 0; i < n; i++) {
if (visited[i] == -1) {
btrack(adjList, visited, dfsCallsNodes, i);
}
}
HashMap<Integer, List<Integer>> adjRevList = new HashMap<>();
for (int i = 0; i < n; i++) {
adjRevList.put(i, new ArrayList<>());
}
for (int i = 0; i < n; i++) {
List<Integer> neighbors = adjList.get(i);
if (neighbors != null) {
for (int neighbor : neighbors) {
adjRevList.get(neighbor).add(i);
}
}
}
Arrays.fill(visited, -1);
int stronglyConnectedComponents = 0;
while (!dfsCallsNodes.isEmpty()) {
int node = dfsCallsNodes.pop();
if (visited[node] == -1) {
List<Integer> newScc = new ArrayList<>();
btrack2(adjRevList, visited, node, newScc);
stronglyConnectedComponents++;
}
}
return stronglyConnectedComponents;
}
}