How to create an array from the contents of a text file to be sorted?

Question

This is a program that takes these three arrays and sorts them using insertion sort and counting the number of comparisons and swaps performed for each array when sorted.

I'm now trying to test three other arrays that have been made on text files. The these three text files are just lists of numbers, the first text file is called "array4.txt" and its list of numbers contains 1 through 2000 in order.

The second file is called "array5.txt" and its list of numbers contains 2000 through 1 in descending order. Lastly, the third file is called "array6.txt" and its list of numbers contains a list of randomly mixed numbers from 1 to 2000, including 1 and 2000 with no repeats.

My goal is to read these files and put their values into an actual array and for my insertion sort method to read them, sort them, and count the number of comparisons and exchanges just as what I did with my first three arrays.

I'm very new to Java and don't know exactly how to do this.

import java.util.Scanner;
import java.io.*;

public class InsertionSort
{
    public static void main(String args[]) throws IOException
    {    
    int[] Array  = {1,2,3,4,5,6,7,8,9,10};  
    int[] Array2 = {10,9,8,7,6,5,4,3,2,1};
    int[] Array3 = {1,10,2,9,3,8,4,7,5,6};

    System.out.println("Insertion Sort: ");
    System.out.println();
    System.out.println("Best Case Scenario: ");
    printArray(Array);
    insertionSort(Array);

    System.out.println("Worst Case Scenario: ");

    printArray(Array2);

    insertionSort(Array2);

    System.out.println("Average Case Scenario: ");
    printArray(Array3);
    insertionSort(Array3);
}

public static void insertionSort(int[] list) 
{
    int comps = 0, swaps = 0;

    for(int i = 1; i < list .length; i++) {

        int j = i;      

        // compare i with sorted elements and insert it
        // sorted elements: [0..i-1]
        while (j > 0 && list[j] < list[j - 1]) {

            int temp = list[j];
            list[j] = list[j - 1];
            list[j - 1] = temp;

            swaps++;
            comps++;  // loop condition true

            j--;
        }
        comps++; // checking loop condition when false
    }
    //printArray(list);

    System.out.println("Comparisons: " + comps 
        + " Swaps: " + swaps);
    System.out.println();
}

static void printArray(int[] array){

    for(int i=0; i < array.length; i++)
    {  
        System.out.print(array[i] + " ");
    } 
    System.out.println();

}

}

Greg. O Hajdu · Accepted Answer · 2018-09-16 03:39:51Z

This is what I came up with. Hope it helps!

package com.company;

import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class Main {

    public static void main(String[] args) throws FileNotFoundException {
        // Replace array.txt with the name of your txt file and your path
        Scanner fileScanner = new Scanner(new File("array.txt"));
        // Counter variable so we'll know the size of the array we'll need
        int counter = 0;
        // Iterate through the file counting the number of integers and incrementing the counter variable
        while(fileScanner.hasNextInt()){
            counter++;
            fileScanner.nextInt();
        }
        // Reset the scanner to the beginning of the txt file
        fileScanner = new Scanner(new File("array.txt"));

        // Scan each integer into the array
        int [] array = new int[counter];
        for (int i = 0; i < array.length; ++i) array[i] = fileScanner.nextInt();
    }
}

Redmancometh · Accepted Answer · 2018-09-16 02:28:36Z

Here you go:

public void getIt() {
    List<Integer> ints = new ArrayList(); //temporary holder

    try (Scanner scanner = new Scanner("filename.txt")) { //open a scanner that will scan our file
        scanner.forEachRemaining(line -> { //iterate through each line in our file
            String[] numberStrings = line.split(","); // the comma is your presumed delimeter IF one exists
            for (int x = 0; x < numberStrings.length; x++) { // loop through each item separated by a comma on each line
                ints.add(Integer.parseInt(numberStrings[x])); // turn this string into an int and add it to your list
            }
        });
    }
    Integer[] integerArray = ints.toArray(new Integer[ints.size()]); //transform our list into an array
}

If it's only one number per line you don't need the for loop or the line.split inside of the forEachRemaining

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