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ShashankSinha98ShashankSinha98
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‎34. Graph 03 - Undirected Graph Problems/Articulation_Point_and_Bridges.java

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import java.util.*;
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public class Articulation_Point_and_Bridges {
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class Pair{
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int a,b;
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Pair(int a, int b){
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this.a = a;
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this.b = b;
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}
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@Override
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public String toString() {
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// TODO Auto-generated method stub
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return "{"+String.valueOf(this.a)+", "+String.valueOf(this.b)+"}";
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}
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}
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class Graph{
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Set<Integer> articulation_points;
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ArrayList<ArrayList<Integer>> arr;
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ArrayList<Pair> bridges;
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int V;
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Graph(int V){
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this.V =V;
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this.arr = new ArrayList<>();
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articulation_points = new HashSet<>();
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bridges = new ArrayList<>();
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for(int i=0;i<V;i++) {
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arr.add(new ArrayList<>());
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}
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}
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public void add_edge(int x, int y) {
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this.arr.get(x).add(y);
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this.arr.get(y).add(x);
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}
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public void display() {
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for(int i=0; i<V; i++) {
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System.out.print(String.valueOf(i));
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for(int j=0;j<this.arr.get(i).size(); j++) {
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System.out.print(" -> "+this.arr.get(i).get(j));
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}
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System.out.println();
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}
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}
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public void points_bridges() {
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int[] discoverTime = new int[this.V];
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int[] lowestTime = new int[this.V];
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int time = 1;
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for(int node=0; node<this.V; node++) {
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if(discoverTime[node]==0) {
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//System.out.println("Time: "+time);
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dfs_helper(node, -1,discoverTime,lowestTime,time);
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}
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}
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//display_arr(discoverTime);
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//display_arr(lowestTime);
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}
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public void dfs_helper(int curr, int parent,int[] discoverTime, int[] lowestTime, int time) {
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int noOfChild = 0;
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discoverTime[curr] = lowestTime[curr] = time;
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time+=1;
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for(int child : this.arr.get(curr)) {
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if(discoverTime[child]==0) {
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noOfChild+=1;
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dfs_helper(child,curr, discoverTime, lowestTime, time);
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lowestTime[curr] = Math.min(lowestTime[curr], lowestTime[child]);
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if(parent!=-1 && lowestTime[child]>=discoverTime[curr]) {
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// AP exist
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//System.out.println("C: "+curr);
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this.articulation_points.add(curr);
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}
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if(lowestTime[child]>discoverTime[curr]) {
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// Bridge exist
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this.bridges.add(new Pair(curr, child));
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}
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} else if(discoverTime[child]>0 && child != parent) {
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lowestTime[curr] = Math.min(lowestTime[curr], discoverTime[child]);
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}
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}
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// Separate case for src node
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if(parent==-1 && noOfChild>=2) {
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this.articulation_points.add(curr);
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}
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}
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public void display_arr(int[] arr) {
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for(int i=0; i<arr.length; i++) {
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System.out.print(arr[i]+", ");
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}
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System.out.println();
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}
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}
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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Graph g1 = new Articulation_Point_and_Bridges().new Graph(5);
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g1.add_edge(0, 1);
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g1.add_edge(1, 2);
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g1.add_edge(2, 0);
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g1.add_edge(2, 3);
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g1.add_edge(3, 4);
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g1.points_bridges();
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System.out.println("Points: "+g1.articulation_points);
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System.out.println("Bridges: "+g1.bridges);
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System.out.println("**************************************");
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Graph g2 = new Articulation_Point_and_Bridges().new Graph(5);
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g2.add_edge(1, 0);
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g2.add_edge(0, 2);
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g2.add_edge(2, 1);
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g2.add_edge(0, 3);
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g2.add_edge(3, 4);
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g2.points_bridges();
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System.out.println("Points: "+g2.articulation_points);
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System.out.println("Bridges: "+g2.bridges);
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System.out.println("**************************************");
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Graph g3 = new Articulation_Point_and_Bridges().new Graph(4);
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g3.add_edge(0, 1);
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g3.add_edge(1, 2);
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g3.add_edge(2, 3);
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g3.points_bridges();
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System.out.println("Points: "+g3.articulation_points);
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System.out.println("Bridges: "+g3.bridges);
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System.out.println("**************************************");
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Graph g4 = new Articulation_Point_and_Bridges().new Graph(7);
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g4.add_edge(0, 1);
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g4.add_edge(1, 2);
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g4.add_edge(2, 0);
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g4.add_edge(1, 3);
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g4.add_edge(1, 4);
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g4.add_edge(1, 6);
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g4.add_edge(3, 5);
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g4.add_edge(4, 5);
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g4.points_bridges();
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System.out.println("Points: "+g4.articulation_points);
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System.out.println("Bridges: "+g4.bridges);
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}
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}

‎35. Graph 04 - Directed Graph Problems/Articulation_Point_and_Bridges.java

Lines changed: 176 additions & 0 deletions
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import java.util.*;
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public class Articulation_Point_and_Bridges {
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class Pair{
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int a,b;
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Pair(int a, int b){
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this.a = a;
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this.b = b;
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}
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@Override
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public String toString() {
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// TODO Auto-generated method stub
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return "{"+String.valueOf(this.a)+", "+String.valueOf(this.b)+"}";
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}
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}
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class Graph{
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Set<Integer> articulation_points;
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ArrayList<ArrayList<Integer>> arr;
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ArrayList<Pair> bridges;
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int V;
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Graph(int V){
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this.V =V;
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this.arr = new ArrayList<>();
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articulation_points = new HashSet<>();
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bridges = new ArrayList<>();
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for(int i=0;i<V;i++) {
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arr.add(new ArrayList<>());
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}
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}
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public void add_edge(int x, int y) {
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this.arr.get(x).add(y);
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this.arr.get(y).add(x);
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}
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public void display() {
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for(int i=0; i<V; i++) {
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System.out.print(String.valueOf(i));
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for(int j=0;j<this.arr.get(i).size(); j++) {
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System.out.print(" -> "+this.arr.get(i).get(j));
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}
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System.out.println();
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}
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}
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public void points_bridges() {
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int[] discoverTime = new int[this.V];
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int[] lowestTime = new int[this.V];
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int time = 1;
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for(int node=0; node<this.V; node++) {
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if(discoverTime[node]==0) {
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//System.out.println("Time: "+time);
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dfs_helper(node, -1,discoverTime,lowestTime,time);
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}
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}
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//display_arr(discoverTime);
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//display_arr(lowestTime);
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}
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public void dfs_helper(int curr, int parent,int[] discoverTime, int[] lowestTime, int time) {
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int noOfChild = 0;
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discoverTime[curr] = lowestTime[curr] = time;
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time+=1;
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for(int child : this.arr.get(curr)) {
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if(discoverTime[child]==0) {
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noOfChild+=1;
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dfs_helper(child,curr, discoverTime, lowestTime, time);
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lowestTime[curr] = Math.min(lowestTime[curr], lowestTime[child]);
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if(parent!=-1 && lowestTime[child]>=discoverTime[curr]) {
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// AP exist
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//System.out.println("C: "+curr);
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this.articulation_points.add(curr);
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}
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if(lowestTime[child]>discoverTime[curr]) {
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// Bridge exist
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this.bridges.add(new Pair(curr, child));
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}
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} else if(discoverTime[child]>0 && child != parent) {
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lowestTime[curr] = Math.min(lowestTime[curr], discoverTime[child]);
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}
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}
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// Separate case for src node
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if(parent==-1 && noOfChild>=2) {
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this.articulation_points.add(curr);
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}
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}
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public void display_arr(int[] arr) {
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for(int i=0; i<arr.length; i++) {
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System.out.print(arr[i]+", ");
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}
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System.out.println();
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}
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}
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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Graph g1 = new Articulation_Point_and_Bridges().new Graph(5);
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g1.add_edge(0, 1);
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g1.add_edge(1, 2);
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g1.add_edge(2, 0);
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g1.add_edge(2, 3);
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g1.add_edge(3, 4);
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g1.points_bridges();
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System.out.println("Points: "+g1.articulation_points);
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System.out.println("Bridges: "+g1.bridges);
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System.out.println("**************************************");
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Graph g2 = new Articulation_Point_and_Bridges().new Graph(5);
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g2.add_edge(1, 0);
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g2.add_edge(0, 2);
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g2.add_edge(2, 1);
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g2.add_edge(0, 3);
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g2.add_edge(3, 4);
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g2.points_bridges();
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System.out.println("Points: "+g2.articulation_points);
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System.out.println("Bridges: "+g2.bridges);
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System.out.println("**************************************");
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Graph g3 = new Articulation_Point_and_Bridges().new Graph(4);
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g3.add_edge(0, 1);
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g3.add_edge(1, 2);
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g3.add_edge(2, 3);
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g3.points_bridges();
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System.out.println("Points: "+g3.articulation_points);
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System.out.println("Bridges: "+g3.bridges);
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System.out.println("**************************************");
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Graph g4 = new Articulation_Point_and_Bridges().new Graph(7);
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g4.add_edge(0, 1);
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g4.add_edge(1, 2);
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g4.add_edge(2, 0);
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g4.add_edge(1, 3);
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g4.add_edge(1, 4);
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g4.add_edge(1, 6);
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g4.add_edge(3, 5);
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g4.add_edge(4, 5);
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g4.points_bridges();
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System.out.println("Points: "+g4.articulation_points);
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System.out.println("Bridges: "+g4.bridges);
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}
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}

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