I've been working on a program to implement a DFS in Java (by taking an adjacency matrix as input from a file). Basically, assuming vertices are traveled in numerical order, I would like to print the order that vertices become dead ends, the number of connected components in the graph, the tree edges and the back edges. But I'm not completely there yet. When I run my program, I get the number "1" as output, and nothing more. I've tried debugging certain parts of the DFS class, but I still can't quite figure out where I'm going wrong. Here is my code:
A basic "Driver" class:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class Driver {
public static void main(String[] args) throws FileNotFoundException {
Scanner scanner = new Scanner(new File("sample1.txt"));
scanner.useDelimiter("[\\s,]+");
int input = scanner.nextInt();
int[][] adjMatrix = new int[8][8];
for(int i=0; i < input; i++) {
for (int j=0; j < input; j++) {
adjMatrix[i][j] = scanner.nextInt();
}
}
scanner.close();
new DFS(adjMatrix);
}
}
DFS class:
import java.util.Stack;
public class DFS {
Stack<Integer> stack;
int first;
int[][] adjMatrix;
int[] visited = new int[7];
public DFS(int[][] Matrix) {
this.adjMatrix = Matrix;
stack = new Stack<Integer>();
int[] node = {0, 1, 2, 3, 4, 5, 6};
int firstNode = node[0];
depthFirstSearch(firstNode, 7);
}
public void depthFirstSearch(int first,int n){
int v,i;
stack.push(first);
while(!stack.isEmpty()){
v = stack.pop();
if(visited[v]==0) {
System.out.print("\n"+(v+1));
visited[v]=1;
}
for (i=0;i<n;i++){
if((adjMatrix[v][i] == 1) && (visited[i] == 0)){
stack.push(v);
visited[i]=1;
System.out.print(" " + (i+1));
v = i;
}
}
}
}
}
And the matrix from the input file looks like this:
0 1 0 0 1 1 0 0
1 0 0 0 0 1 1 0
0 0 0 1 0 0 1 0
0 0 1 0 0 0 0 1
1 0 0 0 0 1 0 0
1 1 0 0 1 0 0 0
0 1 1 0 0 0 0 1
0 0 0 1 0 0 1 0
Take a look at this part:
int input = scanner.nextInt();
int[][] adjMatrix = new int[8][8];
for(int i=0; i < input; i++) {
for (int j=0; j < input; j++) {
adjMatrix[i][j] = scanner.nextInt();
}
}
First you read a number, input.
Then you read input rows, in each row input columns.
This is your input data:
0 1 0 0 1 1 0 0
1 0 0 0 0 1 1 0
0 0 0 1 0 0 1 0
0 0 1 0 0 0 0 1
1 0 0 0 0 1 0 0
1 1 0 0 1 0 0 0
0 1 1 0 0 0 0 1
0 0 0 1 0 0 1 0
What is the first number, that will be read by scanner.nextInt().
It's 0. So the loop will do nothing.
Prepend the number 8 to your input, that is:
8
0 1 0 0 1 1 0 0
1 0 0 0 0 1 1 0
0 0 0 1 0 0 1 0
0 0 1 0 0 0 0 1
1 0 0 0 0 1 0 0
1 1 0 0 1 0 0 0
0 1 1 0 0 0 0 1
0 0 0 1 0 0 1 0
Btw, it's a good idea to verify that you have correctly read the matrix.
Here's an easy way to do that:
for (int[] row : adjMatrix) {
System.out.println(Arrays.toString(row));
}
There are several other issues in this implementation:
The number 7 appears in a couple of places. It's actually a crucial value in the depth-first-search algorithm, and it's actually incorrect. It should be 8. And it should not be hardcoded, it should be derived from the size of the matrix.
It's not a good practice to do computation in a constructor. The purpose of a constructor is to create an object. The depth-first-logic could be moved to a static utility method, there's nothing in the current code to warrant a dedicated class.
Fixing the above issues, and a few minor ones too, the implementation can be written a bit simpler and cleaner:
public static void dfs(int[][] matrix) {
boolean[] visited = new boolean[matrix.length];
Deque<Integer> stack = new ArrayDeque<>();
stack.push(0);
while (!stack.isEmpty()) {
int v = stack.pop();
if (!visited[v]) {
System.out.print("\n" + (v + 1));
visited[v] = true;
}
for (int i = 0; i < matrix.length; i++) {
if (matrix[v][i] == 1 && !visited[i]) {
visited[i] = true;
stack.push(v);
v = i;
System.out.print(" " + (i + 1));
}
}
}
}
Related
I'm reading in numbers to fill an adjacency matrix. The numbers are read in from a file and the format can be seen below.
0 1 0 0 1 1 0 0
1 0 0 0 0 1 1 0
0 0 0 1 0 0 1 0
0 0 1 0 0 0 0 1
1 0 0 0 0 1 0 0
1 1 0 0 1 0 0 0
0 1 1 0 0 0 0 1
0 0 0 1 0 0 1 0
But I'm getting an InputMismatchException when I try to run my program, and I can't figure out why. My code is below. I'd greatly appreciate some help.
import java.util.Scanner;
public class Driver {
public static void main(String[] args) {
Scanner scanner = new Scanner("sample1.txt");
scanner.useDelimiter("[\\s,]+");
int input = scanner.nextInt();
int[][] adjMatrix = new int[8][8];
for(int i=0; i < input; i++) {
for (int j=0; j < input; j++) {
adjMatrix[i][j] = scanner.nextInt();
}
}
scanner.close();
new DFS(adjMatrix);
}
}
I am currently prepping to head into a Data Structures Course and as a result have begun reading on certain topics before hand. I am currently studying up on Stacks but have come across a problem.
I am currently coding a Maze App that uses stacks to auto-solve a maze. However, I am experiencing a problem when it comes populating the maze itself.
Code below:
import java.io.*;
import java.util.*;
public class Maze {
private Square move;
private char[][] maze;
private SquareStack s;
private String path =
"C:\\Users\\Sigh\\workspace\\StegmannStackMaze\\maze.txt";
private File file = new File(path);
public Maze(){
s = new SquareStack();
maze = new char[12][12];
}
public void getMaze() throws IOException{
for (int row = 0; row < 12 ; ++row){ // Creates the left/right walls of the maze " | | "
maze[row][0] = '1';
maze[row][11] = '1';
}
for ( int col = 0; col < 12 ; ++col){ // Creates upper and lower walls of the maze
maze[0][col] = '1';
maze[11][col] = '1';
}
Scanner filescan = new Scanner(path);
for( int row = 1; row <= 10 ; ++row){
String line = filescan.nextLine();
String delim = "[ ]+";
String[] tokens = line.split(delim);
for(int col = 1; col <= 10; ++col)
maze[row][col] = tokens[col-1].charAt(0);
}
filescan.close();
}
}
Here is the .txt file
0 0 1 E 1 0 0 1 1 1
0 1 1 0 1 0 1 0 0 0
0 0 0 0 0 0 0 0 1 0
1 1 1 1 1 0 1 1 0 0
0 0 0 1 0 0 0 1 0 1
0 1 0 1 0 1 1 1 0 1
0 1 0 1 0 0 0 1 0 0
1 1 0 1 1 1 0 1 1 0
0 1 0 0 0 0 0 1 1 0
0 1 0 1 1 0 1 0 0 0
The Exception itself occurs at this particular line once col = 2.
for(int col = 1; col <= 10; ++col)
maze[row][col] = tokens[col-1].charAt(0);
}
From what I gather, this line takes each token that is created and populates the column. However, I am not sure why I get a exception.
Thanks for reading and hopefully I can get some insight from you guys.
Changes
Scanner filescan = new Scanner(path);
to
Scanner filescan = new Scanner(file);
The path is a String variable rather than File instance.
I'm trying to get an output of a random string consisted of 1's and 0's in a Matrix style. I know how to display a string consisted of 1's and 0's, but I can't keep on looping through it for some reason. What I'm trying to do, is that whenever the StringBuilder reaches the length of 20, I want to start the loop on a new line again and repeat this 100 times.
import java.util.List;
import java.util.Random;
public class main {
static Random rand = new Random();
static StringBuilder x = new StringBuilder();
static int a = 0;
public static void main(String[] args) {
generatingnumber();
}
public static void generatingnumber() {
for (int bv = 0; bv <= 100; bv++) {
int random = rand.nextInt(50);
if (random % 2 == 0) {
x.append(" 0");
} else {
x.append(" 1");
}
if (x.length() == 20) {
System.out.println(x);
}
}
}
}
public class MatrixFilm {
public static void main(String[] args) {
int rows = 100;
int cols = 20;
for (int count1 = 0; count1 < (rows * cols); count1++) {
for (int count2 = 0; count2 < cols; count2++) {
int randomNum = 0 + (int) (Math.random() * 2);
System.out.print(" " + randomNum);
}
System.out.println();
}
}
}
Result:
0 0 1 0 0 0 0 1 0 0 1 1 0 0 1 0 1 1 1 1
1 1 0 1 1 1 0 1 0 1 0 1 1 0 1 1 0 0 1 0
0 1 0 0 1 0 1 1 0 0 1 1 1 0 1 1 1 1 1 0
0 1 0 1 1 1 1 1 0 0 1 1 0 0 0 1 1 0 1 0
0 0 0 1 0 1 0 0 1 0 0 0 1 0 1 0 0 1 0 0
....
Your string has length of 20 characters only once. You are not interested in whether x.length() == 20 but if x.length() % 20 == 0.
For a new line you can append "\n" (or "\r\n" for Windows machine) to the string, everytime just before printing it.
Change println to print (which doesn't add new line character at the end of printed string) in order to maintain continuity between prints.
Taking all into account:
if (x.length() % 20 == 0) {
x.append("\r\n");
System.out.print(x);
}
However it still wouldn't be enough, for "\r\n" itself adds to the length of the string. This should work:
if (x.length() % 20 == 0) {
x.replace(x.length() - 2, x.length(), "\r\n");
System.out.print(x);
}
You can also - and it would be better to... - reset the string, as #owlstead has mentioned.
if (x.length() == 20) {
System.out.println(x);
x.setLength(0);
}
Anyway; what I presented is not a solution for the problem. Only solution to - probably improper - approach you have currently taken on it.
import java.math.BigInteger;
import java.util.ArrayList;
public class Factorial {
public static int[] bitVector(int n) {
ArrayList<Integer> bitList = new ArrayList<Integer>();
BigInteger input = computeFactorial(n);
System.out.println(input);
BigInteger[] result = input.divideAndRemainder(new BigInteger(String.valueOf(2)));
if (result[0].intValue()==0) {return new int[]{result[1].intValue()};}
else {
bitList.add(result[1].intValue());
}
while(result[0].intValue() != 0) {
result = result[0].divideAndRemainder(new BigInteger(String.valueOf(2)));
bitList.add(result[1].intValue());
}
int[] array = new int[bitList.size()];
for (int i=0; i<array.length; i++) {
array[i]=bitList.get(i).intValue();
}
return array;
}
public static BigInteger computeFactorial(int n) {
if (n==0) {
return new BigInteger(String.valueOf(1));
} else {
return new BigInteger(String.valueOf(n)).multiply(computeFactorial(n-1));
}
}
public static void main(String[] args) {
int[] bitVector = bitVector(35);
for (int bit: bitVector)
System.out.print(bit+" ");
System.out.println();
}
}
The code above works fine when the input to bitVector is no bigger than 35. However, when I pass 36 as a parameter to bitVector, all but one bit are gone in the output.
I have potentially ruled out the following causes:
It may have nothing to do with the BigInteger type since it was designed to never overflow.
It may not be related to memory usage of the program, which uses only 380M at runtime.
I print out the value of computeFactorial(36), which looks good.
What on earth is going on there?
So what you are trying to do is
public static String factorialAsBinary(int n) {
BigInteger bi = BigInteger.ONE;
for (; n > 1; n--)
bi = bi.multiply(BigInteger.valueOf(n));
return bi.toString(2);
}
public static void main(String... args) {
String fact36 = factorialAsBinary(36);
for (char ch : fact36.toCharArray())
System.out.print(ch + " ");
System.out.println();
}
which prints
1 0 0 0 1 0 0 0 1 0 1 0 0 1 1 0 0 0 0 1 0 1 0 1 1 0 0 1 0 1 1 0 1 1 1 1 0 1 1 1 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 0 1 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 0 1 1 0 0 1 1 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
What on earth is going on there?
Your code is much more complicated than it needs to be which also makes it easier to make mistakes and harder to understand.
result[0].intValue() is wrong:
intValue():
Converts this BigInteger to an int. This conversion is analogous to a narrowing primitive conversion from long to int as defined in the Java Language Specification: if this BigInteger is too big to fit in an int, only the low-order 32 bits are returned. Note that this conversion can lose information about the overall magnitude of the BigInteger value as well as return a result with the opposite sign.
in your case it returns the lowest 32 bits which are zero therefore you return 0 after first devision
i want setting an array and below is my code
public static void setArray()
{
int i = 5;
int j = 5;
int testarray[][] = new int[i][j];
for(int x = 0;x<i;x++)
{
for(int y=0;y<j;y++)
{
System.out.print("0 ");
}
System.out.println("");
}
}
the result is something like this:
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
if i want to put a number/alphabet beside to let the user know which column, how can i do that ?
Expected Result:
====================
1 2 3 4 5
A|0 0 0 0 0
B|0 0 0 0 0
C|0 0 0 0 0
D|0 0 0 0 0
E|0 0 0 0 0
You need another initial for-loop to print the numbers, then you need to add another print statement within your second for-loop to print the letter for each row:
System.out.print(" ");
for (int x = 0; x < i; x++) { // this prints the numbers on the first row
System.out.print(" " + x);
}
System.out.println();
for (int x = 0; x < i; x++) {
System.out.print((char) ('A' + x) + "|"); // this prints the letters
for (int y = 0; y < j; y++) {
System.out.print("0 ");
}
System.out.println("");
}
0 1 2 3 4
A|0 0 0 0 0
B|0 0 0 0 0
C|0 0 0 0 0
D|0 0 0 0 0
E|0 0 0 0 0
You need to print 1, 2, 3, 4, 5 .. column number of times and print A, B, C, D .. till you reach the number of rows. Try coding it yourself, it's not that difficult (I don't want to provide a ready-made code)