在Java中的double数组中查找最频繁的值（无哈希图或排序）

Question

Write a full Java program that does the following:

• Creates an array of 100 double.

• Reads in an unknown number of doubles from a file named values.txt .

• There will be at least 2 distinct values, and no more than 100 distinct values in the file. The values will be in unsorted order. Values will be no smaller than 0, and no larger than 99.

• Outputs the most frequently occurring value in the file.

• Outputs the least frequently occurring value in the file. The value must occur at least once in order to be output.

• Outputs the average of all array values.

• You must create and use separate methods for each of the items #2-5.

This is what I have so far. I cannot for the life of me figure out how to get this right:

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

public class arrayProgram2 {

    static Scanner console = new Scanner(System.in);
    static final int ARRAY_SIZE = 100;
    static int numOfElements = 0;

    public static void main(String[] args) throws FileNotFoundException {
        Scanner inFile = new Scanner(new FileReader("values.txt"));
        double[] Arr1 = new double[ARRAY_SIZE];

        while (inFile.hasNext()) {
            Arr1[numOfElements] = inFile.nextDouble();
            numOfElements++;
        }

        System.out.println("There are " + numOfElements + " values.");
        System.out.printf("The average of the values is %.2f%n", avgArray(Arr1));
        System.out.println("The sum is " + sumArray(Arr1));

        inFile.close();

    } //end main

    //Method to calculate the sum
    public static double sumArray(double[] list) {
        double sum = 0;

        for (int index = 0; index < numOfElements; index++) {
            sum = sum + list[index];
        }

        return sum;
    }

    //Method to calculate the average
    public static double avgArray(double[] list) {
        double sum = 0;
        double average = 0;

        for (int index = 0; index < numOfElements; index++) {
            sum = sum + list[index];
        }

        average = sum / numOfElements;
        return average;
    }
} //end program

Notice I am required to make an array of double even though it is not necessary.

Answer 1

If all values are int than you should use int array instead of double . As all values in range 0-99. So, you can increase input value frequency. Look at below logic:

 int[] freqArr= new int[100];
 while (inFile.hasNext()){
   int value = inFile.nextInt();
   freqArr[value]++;  // count the frequency of selected value.
 } 

Now calculate the maximum frequency from freqArr

 int maxFreq=0;
 for(int freq : freqArr){
   if(maxFreq < freq){
      maxFreq = freq;
   }
 }

Note: If double array is mandatory than you can also use double array like:

 double[] freqArr= new double[100];
 while (inFile.hasNext()){
   freqArr[(int)inFile.nextDouble()]++;
 }

Answer 2

It's possible to find a most-occurring value without sorting like this:

static int countOccurrences(double[] list, double targetValue) {
    int count = 0;
    for (int i = 0; i < list.length; i++) {
        if (list[i] == targetValue)
            count++;
    }
}


static double getMostFrequentValue(double[] list) {
    int mostFrequentCount = 0;
    double mostFrequentValue = 0;
    for (int i = 0; i < list.length; i++) {
        double value = list[i];
        int count = countOccurrences(list, value);
        if (count > mostFrequentCount) {
            mostFrequentCount = count;
            mostFrequentValue = value;
        }
    }
    return mostFrequentValue;
}

Answer 3

Pham Thung is right : - You read in integer inFile.nextInt(), why do you need to use double array to store them? – Pham Thung

You can achieve your first functionality in n time if its integer array.

you question says,

Values will be no smaller than 0, and no larger than 99.

So, 1. Make an array of size 100.(Counter[]) 2. Iterate through values of your current array and add count to Counter array.

eg: if double array contains 2 3 2 5 0 0 0

Our counter array will be like
location : 0 1 2 3 4 5 6 ...........100

values : 3 0 1 1 0 1 0 ..............

and so on.

Answer 4

You can use below algorithm for this

1. Sort the array (you only need to read unsorted array, but you can sort the array once read from the file)
2. Make double var : num, mostCommon, count = 0, currentCount = 1
3. Assign Arr1[0] to num

4. for i from 1 to length of Arr1

   i. if(Arr1[i] == num)

   a. Increment currentCount

   ii. else

   a. if(count > currentCount)

   A. Assign currentCount to count

   B. Assign num to mostCommon

   C. Assign Arr1[i] to num

   D. Assign 1 to currentCount

At the end of this loop, you will have most common number in mostCommon var and it's number of occurrence in count.

Note : I don't know how to format the algo