ArticulationPoint.java

import java.util.*;
public class Articulation {
private int n;
private int[][] arr;
private int[] dfn;
private int[] low;
private int num;
private Set<Integer> s;
public Articulation(int n) {
this.n = n;
arr = new int[n][n];
dfn = new int[n];
low = new int[n];
num = 1;
s = new HashSet<>();
}
public void read(Scanner scan) {
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++)
arr[i][j] = scan.nextInt();
dfn[i] = 0;
}
}
public void art(int u, int v) {
dfn[u] = num;
low[u] = num;
num++;
int child = 0;
for (int j = 0; j < n; j++) {
if (arr[u][j] == 1 && dfn[j] == 0) {
if (v == -1)
child++;
art(j, u);
if (v != -1 && low[j] >= dfn[u])
s.add(u);
low[u] = Math.min(low[u], low[j]);
} else if (arr[u][j] == 1 && j != v)
low[u] = Math.min(low[u], dfn[j]);
}
if (v == -1 && child > 1)
s.add(u);
}
public void printVisited() {
System.out.println("articulation points" + s);
for (int i = 0; i < n; i++)
System.out.print(dfn[i] - 1 + " ");
System.out.println();
}
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
System.out.println("enter no of vertices");
int n = scan.nextInt();
Articulation art = new Articulation(n);
System.out.println("adjacent matrix");
art.read(scan);
art.art(0, -1);
System.out.println("vertices");
art.printVisited();
}
}

OUTPUT:
enter no of vertices
5
adjacent matrix
0 1 1 0 0
1 0 1 0 0
1 1 0 1 0
0 0 1 0 1
0 0 0 1 0
vertices
articulation points[2, 3]
0 1 2 3 4