DFS.java

import java.util.*;

/**
 * Implementation of a Depth First Search
 * 
 * @author Unknown
 *
 */

public class DFS{
	
	/**
	 * Implementation in code of a DFS
	 * 
	 * @param a structure to be DFS'ed
	 * @param vertices The vertices
	 * @param source The source
	 */
	public static void dfsImplement(byte [][] a,int vertices,int source){            //passing adjacency matrix and no of vertices
		byte []b=new byte[vertices];               //flag container containing status of each vertices
		Arrays.fill(b,(byte)-1);                  //status initialization
		/*       code   status 
		          -1  =  ready
		           0  =  waiting
		           1  =  processed       */
		
		
		Stack st=new Stack(vertices);         //operational stack
		st.push(source);                          //assigning source
		while(!st.isEmpty()){
			b[st.peek()]=(byte)0;                 //assigning waiting status
			System.out.println(st.peek());
			int pop=st.pop();
			b[pop]=(byte)1;                       //assigning processed status
			for(int i=0;i<vertices;i++){
				if(a[pop][i]!=0 && b[i]!=(byte)0 && b[i]!=(byte)1 ){
					st.push(i);
					b[i]=(byte)0;                  //assigning waiting status
				}}}
		
	}
	
	/**
	 * The main method
	 * 
	 * @param args Command line arguments
	 */
	public static void main(String args[]){
		Scanner in=new Scanner(System.in);
		int vertices=in.nextInt(),source=in.nextInt();
		byte [][]a=new byte [vertices][vertices];
		//initially all elements of a are initialized with value zero
		
		for(int i=0;i<vertices;i++){
			int size =in.nextInt(); 
			for(int j=0;j<size;j++){
				a[i][in.nextInt()]=1;      //taking adjacency entries by assigning 1
			}
		}
		dfsImplement(a,vertices,source);         //function call
		in.close();
	}
}