Shellsorting an array from an input file

问题

The full project is to take data in from a file which is a text file containing a list of all 201 countries and their respective rates of internet use in alphabetical order. Here is an example

Afghanistan                 7
Albania                    63
Algeria                    20
Andorra                    97
Angola                     23
...

With this we have to Shellsort (specifically) the data numerically. I have successfully done this but I only am outputting a list of the percentages, where as I need the countries listed as well. Here is my code:

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

public class InternetUsers {
public static void main(String[] args) throws IOException{
    // TODO Auto-generated method stub

    String populationString = "";
    String[] line = new String[201];
    int populations[] = new int[201];   

    Scanner fileIN = new Scanner(new File("F:/CountrySortedAlpha.txt"));

    while(fileIN.hasNext()){
        for(int i = 0; i < 201; i++){
            populationString = fileIN.nextLine().substring(26, 29);
            populations[i] = Integer.parseInt(populationString.trim());
        }   
        int j;
            for(int gap = populations.length / 2; gap > 0; gap /= 2){
                for (int k = 0; k < populations.length; k++){   
                }
                for (int t = gap; t < populations.length; t++){
                    int tmp = populations[t];
                        for(j = t; j >= gap && (tmp < populations[j - gap]); j -= gap){
                            populations[j] = populations[j - gap];
                        }
                        populations[j] = tmp;
                }
        }
        System.out.println("\nFinal sorted order: ");
        for(int k = 0; k < populations.length; k++){
            System.out.print(populations[k]);
            System.out.println("");
        }
        System.out.println();
    }   
}
}

So my question is how am I to go about outputting the countries as well? do I need to completely redo the way I sorted? Here is my sample output:

 Final sorted order: 
 1
 1
 2
 2
 2
 2
 2
 3
 ....

回答1:

When you parse the file, you need to store parsed value in a dictionary or some other structure. After you sort, when printing, read the values from dictionary.

I modified you code to store values in a dictionary, and added comments to the lines I added/modified. I did not touch your sorting algo, so you are still sorting on the same array:

public static void main(String[] args) throws IOException {
    String populationString = "";
    String[] line = new String[201];
    int populations[] = new int[201];

    // Have a dictionary that can store the values you parse
    Map<Integer, String> dictionary = new HashMap<Integer, String>();

    Scanner fileIN = new Scanner(new File("F:/CountrySortedAlpha.txt"));

    while (fileIN.hasNext()) {
        for (int i = 0; i < 201; i++) {
            // Parse the whole line, this 29 hard coded seems incorrect
            populationString = fileIN.nextLine().substring(0, 29);
            // Grab both values
            String[] splited = populationString.split("\\s+");
            // Country name can have spaces, so take the last elemnt
            populations[i] = Integer.parseInt(splited[splited.length - 1]);
            // Join back values
            String country = populationString.join(" ", splited);
            // Cut off the rate number
            country = country.substring(0, country.lastIndexOf(" "));
            // Store them in your dictionary
            if (dictionary.containsKey(populations[i])) {
                // If multiple countries have same rate, add them to value, and separate with comma
                String value = dictionary.get(populations[i]);
                dictionary.put(populations[i], value + "," + country);
            } else {
                dictionary.put(populations[i], country);
            }
        }
        int j;
        for (int gap = populations.length / 2; gap > 0; gap /= 2) {
            for (int t = gap; t < populations.length; t++) {
                int tmp = populations[t];
                for (j = t; j >= gap && (tmp < populations[j - gap]); j -= gap) {
                    populations[j] = populations[j - gap];
                }
                populations[j] = tmp;
            }
        }
        System.out.println("Final sorted order: ");
        for (int k = 0; k < populations.length; k++) {
            // Read the value from dictionary
            String value = dictionary.get(populations[k]);
            // For duplicates skip, that entry gets deleted after values were printed
            if (value == null) {
                continue;
            }

            // If multiple countries had the same rate, they were stored as comma separated value
            String[] countries = value.split(",");
            for (String country : countries) {
                // You can print rate, or country, or both
                System.out.println(populations[k] + " " + country);
            }

            // Remove from dictionary, because we already printed all countries with the same rate
            dictionary.remove(populations[k]);
        }
        System.out.println();
    }

    // Don't forget to close the file
    fileIN.close();
}

回答2:

Unless prof. said specifically do it with an array of Strings for the countries and an array of ints for the rates, @ScaryWombat's idea of an array of objects each containing a String and an int is the way to go.

That being said, you could still do it with the separate arrays if you must. Just be sure to swap both the line and the population entries when your sort algorithm calls for a swap, not only the population entry.

来源：https://stackoverflow.com/questions/43728432/shellsorting-an-array-from-an-input-file

标签

java

algorithm

data-structures

shellsort