如何查找名称在列表中重复的次数？

Question

I wrote a code for finding how many times a name is repeated in an array, there is some issue with it.

I need this to be done without any kind of collections framework (Maps, Set or Array) and only targeting to solve this by loops only.

package string;
import java.util.*;
public class CountingNames {

    public static void main(String[] args) {
        int i,j,t,c;
        String a[]=new String[10];
        String b[]=new String[10];
        Scanner sc=new Scanner(System.in);
        for(i=0;i<10;i++)
        {
            a[i]=sc.nextLine();
            b[i]=a[i];
        }
        int len=b.length;
        for(i=0;i<len;i++)
        {
            c=1; //Setting Counter
            for(j=i+1;j<len-1;j++)
            {
                if(b[i].equals(b[j]))
                {
                    c++;
                    for(t=j;t<len-1;t++)
                    {
//Deleting the repeated element by replacing with the next element
                        b[t]=b[t+1];
                    }
                }
            }
             System.out.println(b[i]+" is repeated "+ c +" times ");
             len-=c-1; //Decreasing the loop by the number of times the element has been repeadted
       }
   }

}

INPUT:

HAROLD
HAROLD
HAROLD
JAVA
JOKER
HOLD
JAVA
KOI
JAVA
GOAT

OUTPUT:

HAROLD is repeated 2 times 
HAROLD is repeated 1 times 
JAVA is repeated 3 times 
JOKER is repeated 1 times 
HOLD is repeated 1 times 
KOI is repeated 1 times 
GOAT is repeated 1 times 

Answer 1

First of all, some general tips: Avoid declaring several variables in one line. This doesn't help readability.

Secondly, please always provide significant names to your variables, especially if you intend to get help from other people. We cannot tell what a variable named p is supposed to do. i and j are OK to indicate index, but for anything else, use significant names.

Lastly, it is a bad practice to declare iterators outside of for loops. Always try to declare and initialize your iterator variables inside the for loop. This will avoid many headaches when your code is large and you won't lose track of something like i .

Now, your code could use some further refactoring. A second array is totally unnecessary.

public class CountWords {
   public static void calculate(){
            
      String a[]=new String[10];
      Scanner sc=new Scanner(System.in);
      for(int i = 0; i < a.length; i++)
      {
           System.out.println("Enter word: ");
           a[i]=sc.nextLine();
      }
            
      for(int i=0;i< a.length; i++)
      {
         int count = 1;
         /*rather than having a 2nd array, we can simply 
         have a nested for loop where the index starts at 1.
         you'll always be comparing the current element with the         
         next one.
         */
         for(int j = 1;j< a.length;j++)
         {
           if(a[i].equals(a[j]))
           {
            count++;
           }
         }
         System.out.println(a[i]+" is repeated "+ count +" times ");
       }
   }
  

}

Keep in mind that this will print the results repeated, that is to say, an input of HAROLD * 3 will result in the output being "COUNT FOR HAROLD IS 3" printed three times.

If you wish to strictly count the amount of times a word is repeated , that is, we don't care about its first occurrence, then initialize count to 0 rather than 1.

This is not an ideal use for arrays. If there is no actual reason preventing you from using collections, you should absolutely use a HashMap for this type of problems to avoid the re-print of values.

As a possible workaround, you may try adding another for loop at the beginning, to count the unique words you have in your array. Store the amount in an int variable, then, create a new array with the size of that variable, and instead of printing into the console, add the word count result to a string, then proceed to insert that string into the uniqueWords array, using similar logic to NOT insert the count message if its already present in the uniqueWords array. Lastly, iterate through this uniqueWords array to print its elements.

As to why your code failed: In your T for loop, You were reassigning the items in your B array to be the next element.

So, it worked twice for Harold because B[t] was Harold, and B[t+1] was Harold as well. But for the third iteration, B[t] is Harold and B[t+1] is Java. Therefore, only one instance of Harold was found and the previous Harolds had been overwritten by the reassignment.

Answer 2

Instead of looping, you can use Map like below

//Assuming you have array "names" containing names
String[] names = new String[10];
Map<String,Integer> countMap = new HashMap<String,Integer>();
for(int i=0;i<names.length;i++) {
     
     if(countMap.get(names[i]) != null)
         countMap.put(names[i],countMap.get(names[i])+1);
     else
         countMap.put(names[i],1);
 }
//Print your frequencies

for(Map.Entry<String,Integer> entry : countMap.entrySet()) {
     
     System.out.println(entry.getKey()+" is repeated "+entry.getValue()+ " times.");
}

Answer 3

You can use a single array and a hash map to find the number of times the items are repeated. In the below solution, I loop over the String array 'a' once and populate a HashMap with the String value and then I either calculate the value by incrementing it, or I assign it the value of 1. I can then loop over the HashMap key set (all the string values) and then print out their values which will be ht number of times they are repeated.

Map<String, Integer> mapOfNames = new HashMap<>();
        for(String s: a){
            if(mapOfNames.containsKey(s)){
                mapOfNames.put(s, mapOfNames.get(s) + 1);
            }
            else{
                mapOfNames.put(s, 1);
            }
        }

        for(String s : mapOfNames.keySet()){
            System.out.println(s + " is repeated " + mapOfNames.get(s) + " times.");
        }

Will print:

JAVA is repeated 3 times.
JOKER is repeated 1 times.
KOI is repeated 1 times.
HAROLD is repeated 3 times.
GOAT is repeated 1 times.
HOLD is repeated 1 times.

Answer 4

public class App {
    public static void main(String[] args) {
        int i,j;
        String a[]=new String[10];
        boolean b[]=new boolean[10];
        Scanner sc=new Scanner(System.in);

        for(i=0; i<10; i++ ) {
            System.out.print(">>>");
            a[i]=sc.nextLine();
            b[i]=false;
        }

        for(i=0; i<10; i++ ) {
            int count = 0;

            if (!b[i]) {
                for(j=0 ; j<10 ; j++ ) {
                    if (a[i].equals(a[j])) {
                        count++;
                        b[j]=true;
                    }
                }
                System.out.println(a[i] + " is repeated " + (count-1) + " times" );
                // If you need the number of times the name appeared then use the below line
                // System.out.println(a[i] + " is repeated " + (count) + " times" );
            }
        }
   }
}

If you need the number of times the name appeared in the list the use

System.out.println(a[i] + " is repeated " + (count) + " times" );

Or if you want the number of time the name is repeated, then use

System.out.println(a[i] + " is repeated " + (count-1) + " times" );

Input:-

HAROLD
HAROLD
HAROLD
JAVA
JOKER
HOLD
JAVA
KOI
JAVA
GOAT

Output:-

HAROLD is repeated 2 times
JAVA is repeated 2 times
JOKER is repeated 0 times
HOLD is repeated 0 times
KOI is repeated 0 times
GOAT is repeated 0 times