java - 在 Java 中运行稳定婚姻算法时难以读取 .txt 数据

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我是 Java 新手，我正在尝试执行下面有关稳定 Marrage 算法的代码，但是在执行下面的代码时出现以下错误:

Error: For input string: "3 " Exception in thread "main" java.lang.NullPointerException at br.com.entrada.GaleShapley.(GaleShapley.java:21) at br.com.entrada.GaleShapley.main(GaleShapley.java:166)

Gale Shapley 婚姻算法

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;

public class GaleShapley
{
private int N, engagedCount;
private String[][] menPref;
private String[][] womenPref;
private String[] men;
private String[] women;
private String[] womenPartner;
private boolean[] menEngaged;

/** Constructor **/
public GaleShapley(String[] m, String[] w, String[][] mp, String[][] wp)
{
    N = mp.length;
    engagedCount = 0;
    men = m;
    women = w;
    menPref = mp;
    womenPref = wp;
    menEngaged = new boolean[N];
    womenPartner = new String[N];
    calcMatches();
}
/** function to calculate all matches **/
private void calcMatches()
{
    while (engagedCount < N)
    {
        int free;
        for (free = 0; free < N; free++)
            if (!menEngaged[free])
                break;

        for (int i = 0; i < N && !menEngaged[free]; i++)
        {
            int index = womenIndexOf(menPref[free][i]);
            if (womenPartner[index] == null)
            {
                womenPartner[index] = men[free];
                menEngaged[free] = true;
                engagedCount++;
            }
            else
            {
                String currentPartner = womenPartner[index];
                if (morePreference(currentPartner, men[free], index))
                {
                    womenPartner[index] = men[free];
                    menEngaged[free] = true;
                    menEngaged[menIndexOf(currentPartner)] = false;

                }
            }
        }            
    }
    printCouples();
}
/** function to check if women prefers new partner over old assigned partner **/
private boolean morePreference(String curPartner, String newPartner, int index)
{
    for (int i = 0; i < N; i++)
    {
        if (womenPref[index][i].equals(newPartner))
            return true;
        if (womenPref[index][i].equals(curPartner))
            return false;
    }
    return false;
}
/** get men index **/
private int menIndexOf(String str)
{
    for (int i = 0; i < N; i++)
        if (men[i].equals(str))
            return i;
    return -1;
}
/** get women index **/
private int womenIndexOf(String str)
{
    for (int i = 0; i < N; i++)
        if (women[i].equals(str))
            return i;
    return -1;
}
/** print couples **/
public void printCouples()
{
    System.out.println("Couples are : ");
    for (int i = 0; i < N; i++)
    {
        System.out.println(womenPartner[i] +" "+ women[i]);
    }
}
/** main function **/
public static void main(String[] args) 
{
    System.out.println("Gale Shapley Marriage Algorithm\n");
    /** list of men **/
    String[] m = {"1", "2", "3"};
    /** list of women **/
    String[] w = {"1", "2", "3"};

    /** men preference **/


    String[][] mp = null ;
    /** women preference **/                      
    String[][] wp= null ;

 // Input.txt is like
 // 3 <--defines the size of array
 // male preference array
 // 1 3 2
 // 1 2 3
 // 2 3 1

//female preference array
//1 3 2
//2 1 3
//2 1 3


    try{
      FileInputStream fstream = new FileInputStream("input.txt");
      DataInputStream in = new DataInputStream(fstream);
      BufferedReader br = new BufferedReader(new InputStreamReader(in));
      String strLine;
      int line=0;
      int k=0;
      int n=0;
      int i=0;
      while ((strLine = br.readLine()) != null) {
         if(line==0){
            n =Integer.valueOf(strLine);
            mp=new String[n][n];
            wp=new String[n][n];
            line++;
         }
         else{

             String[] preferences=strLine.split(" ");

             if(i<n){
                 mp[i]=preferences;
             }
             else{
                 wp[i-n]=preferences;
             }
             i++;
         }
      }
      in.close();

        }catch (Exception e){//Catch exception if any
              System.err.println("Error: " + e.getMessage());
        }
    GaleShapley gs = new GaleShapley(m, w, mp, wp);                        
   }
  }

程序未完全读取 input.txt 输入文件。它仅读取该文件的第一行。而我无法解决这个问题。我认为问题应该出在下面的代码部分。

while ((strLine = br.readLine()) != null) {
         if(line==0){
            n =Integer.valueOf(strLine);
            mp=new String[n][n];
            wp=new String[n][n];
            line++;
         }
         else{

             String[] preferences=strLine.split(" ");

             if(i<n){
                 mp[i]=preferences;
             }
             else{
                 wp[i-n]=preferences;
             }
             i++;
         }
      }

下面是输入文件:input.txt

3 
male preference array
1 3 2
1 2 3
2 3 1

female preference array
1 3 2
2 1 3
2 1 3

Answer 1

由于以下原因引发错误:3 => 它包含空格 当您调用 Integer.parse(N) 时，由于存在空格，N 无法解析为 Integer ,

为了解决这个问题，我使用了strLine.trim();

women[i].equals(str) : you are comparing here a string to an Integer is always false and the result of your function womenIndexOf is -1, and this is going to throw an exception of IndexOutOfBounds Exception when using the -1 as index

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;

public class GaleShapley {
    private int N, engagedCount;
    private String[][] menPref;
    private String[][] womenPref;
    private String[] men;
    private String[] women;
    private String[] womenPartner;
    private boolean[] menEngaged;

    /** Constructor **/
    public GaleShapley() {

    }

    public GaleShapley(String[] m, String[] w, String[][] mp, String[][] wp) {
        N = mp.length;
        engagedCount = 0;
        men = m;
        women = w;
        menPref = mp;
        womenPref = wp;
        menEngaged = new boolean[N];
        womenPartner = new String[N];
        calcMatches();
    }

    /** function to calculate all matches **/
    private void calcMatches() {
        while (engagedCount < N) {
            int free;
            for (free = 0; free < N; free++)
                if (!menEngaged[free])
                    break;

            for (int i = 0; i < N && !menEngaged[free]; i++) {
                int index = womenIndexOf(menPref[free][i]);
                if (womenPartner[index] == null) {
                    womenPartner[index] = men[free];
                    menEngaged[free] = true;
                    engagedCount++;
                } else {
                    String currentPartner = womenPartner[index];
                    if (morePreference(currentPartner, men[free], index)) {
                        womenPartner[index] = men[free];
                        menEngaged[free] = true;
                        menEngaged[menIndexOf(currentPartner)] = false;

                    }
                    engagedCount++;

                }

            }
        }
        printCouples();
    }

    /** function to check if women prefers new partner over old assigned partner **/
    private boolean morePreference(String curPartner, String newPartner, int index) {
        for (int i = 0; i < N; i++) {
            if (womenPref[index][i].equals(newPartner))
                return true;
            if (womenPref[index][i].equals(curPartner))
                return false;
        }
        return false;
    }

    /** get men index **/
    private int menIndexOf(String str) {
        for (int i = 0; i < N; i++)
            if (men[i].equals(str))
                return i;
        return -1;
    }

    /** get women index **/
    private int womenIndexOf(String str) {
        for (int i = 0; i < N; i++) {
            if (women[i].equals(str))
                return i;
        }

        return -1;
    }

    /** print couples **/
    public void printCouples() {
        System.out.println("Couples are : ");
        for (int i = 0; i < N; i++) {
            System.out.println(womenPartner[i] + " " + women[i]);
        }
    }

    /** main function **/
    public static void main(String[] args) {
        System.out.println("Gale Shapley Marriage Algorithm\n");
        /** list of men **/
        String[] m = { "1", "2", "3" };
        /** list of women **/
        String[] w = { "1", "2", "3" };

        /** men preference **/

        String[][] mp = null;
        /** women preference **/
        String[][] wp = null;

        try {
            FileInputStream fstream = new FileInputStream("C:\\Users\\Youssef\\Projects\\STS\\TEST\\src\\input");
            DataInputStream in = new DataInputStream(fstream);
            BufferedReader br = new BufferedReader(new InputStreamReader(in));
            String strLine;
            int line = 0;
            int n = 0;
            int i = 0;
            while ((strLine = br.readLine()) != null) {
                if (line == 0) {
                    n = Integer.valueOf(strLine.trim());
                    mp = new String[n][n];
                    wp = new String[n][n];
                    line++;
                } else {
                    if (strLine != null && !strLine.equals("") && !strLine.contains("male")
                            && !strLine.contains("female")) {
                        String[] preferences = strLine.split(" ");

                        if (i < n) {
                            mp[i] = preferences;
                        } else {
                            if (i - n < w.length) {
                                wp[i - n] = preferences;

                            }
                        }
                        i++;
                    }

                }
            }
            in.close();

            new GaleShapley(m, w, mp, wp);

        } catch (Exception e) {// Catch exception if any
            e.printStackTrace();
            System.err.println("Error: " + e.getMessage());
        }
    }

}