CodeGym/Help with Java Tasks/On paper everything looks fine however when I Verify Task...

Level 41

05.11.2020
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On paper everything looks fine however when I Verify Task, second to last condition not met (duplicates are not removed) . :(

Question about the task

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Hi, as written in the title, the second to last condition is not fulfilled. I have gone through the program on paper and pen and for me it makes sense, it should work. Also, when I run the three lines in void main, for line " //removeFirstNameDuplicates(createMap()); " I get the attached error.

public class Solution {

    public static HashMap<String, String> createMap() {
        //write your code here
        HashMap<String, String> namesMap = new HashMap<>();
        for (int i = 0; i < 8; i++){
            namesMap.put(i+"lastName", "firstName"+i+1);
        }
        namesMap.put("lastName", "firstNameSame");
        namesMap.put("lastName1", "firstNameSame");
        return namesMap;
    }


    public static void removeFirstNameDuplicates(Map<String, String> map) {
        //write your code here
        Iterator<Map.Entry<String,String>> iteratorForFirstName = map.entrySet().iterator();

        while (iteratorForFirstName.hasNext())
        {
          Map.Entry<String, String> firstMapPair = iteratorForFirstName.next();

          String firstPairValue = firstMapPair.getValue();

          int count = Collections.frequency(map.values(), firstPairValue);

          if (count > 0)
          {
            removeItemFromMapByValue(map, firstPairValue);
            count = 0;
          }

        }
    }

    public static void removeItemFromMapByValue(Map<String, String> map, String value) {
        HashMap<String, String> copy = new HashMap<String, String>(map);
        for (Map.Entry<String, String> pair : copy.entrySet()) {
            if (pair.getValue().equals(value))
                map.remove(pair.getKey());
        }
    }

    public static void main(String[] args) {
        //System.out.println(createMap());
        //removeFirstNameDuplicates(createMap());
        //System.out.println(createMap());

    }
}

Create a Map<String, String> and add ten entries that represent (last name, first name) pairs.
Remove people with the same first name.

Requirements:

The program should not display text on the screen.
The program should not read values from the keyboard.
The createMap() method must create and return a HashMap that has (String, String) elements and contains 10 entries.
The removeFirstNameDuplicates() method must remove from the map all people who have the same first name.
The removeFirstNameDuplicates() method must call the removeItemFromMapByValue() method.

package com.codegym.task.task08.task0817; import java.util.Collections; import java.util.HashMap; import java.util.Iterator; import java.util.Map; /* We don't need repeats */ public class Solution { public static HashMap<String, String> createMap() { //write your code here HashMap<String, String> namesMap = new HashMap<>(); for (int i = 0; i < 8; i++){ namesMap.put(i+"lastName", "firstName"+i+1); } namesMap.put("lastName", "firstNameSame"); namesMap.put("lastName1", "firstNameSame"); return namesMap; } public static void removeFirstNameDuplicates(Map<String, String> map) { //write your code here Iterator<Map.Entry<String,String>> iteratorForFirstName = map.entrySet().iterator(); while (iteratorForFirstName.hasNext()) { Map.Entry<String, String> firstMapPair = iteratorForFirstName.next(); String firstPairValue = firstMapPair.getValue(); // for (String valueForComparison : map.values()) int count = Collections.frequency(map.values(), firstPairValue); /* if (firstPairValue.equals(map.get(valueForComparison))) { count++; } */ if (count > 0) { removeItemFromMapByValue(map, firstPairValue); count = 0; } //condition to delete the keys whose values are repeated; } } public static void removeItemFromMapByValue(Map<String, String> map, String value) { HashMap<String, String> copy = new HashMap<String, String>(map); for (Map.Entry<String, String> pair : copy.entrySet()) { if (pair.getValue().equals(value)) map.remove(pair.getKey()); } } public static void main(String[] args) { // System.out.println(createMap()); // removeFirstNameDuplicates(createMap()); // System.out.println(createMap()); } }

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Dmitri

Level 22 , Seversk, Russia

5 November 2020, 12:41

useful

what number .frequency returns if there is one original element?

Andrei

Level 41

5 November 2020, 13:31

I believe 1 ? Not sure. What do you think?

Andrei

Level 41

5 November 2020, 13:54

Definitely 1, because I used your input and Misiu's and while count was 0 I still had the error. When made count 1 the program passed succesfully!

Misiu

Level 41 , Gdansk, Poland

5 November 2020, 12:07

solution

Changing a map while iterating it gives the exception. Create a copy of map. Iterate copy, remove from map. Look at removeItemFromMapByValue() how this is working.

Andrei

Level 41

5 November 2020, 13:55

Ah! OK, haha that finally makes sense! Yes, thank you! I also had to modify count to initial value 1 because having it to 0 would still not pass testing. Thank you again! :D

Andrei

Level 41

5 November 2020, 13:59

This is the final version. But strange thing happens when I run void main. It does not eliminate the duplicates, which are "firstNameSame".. the outputted values are the same. Do you know why?

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/*
We don't need repeats

*/

public class Solution {

    public static HashMap<String, String> createMap() {
        //write your code here
        HashMap<String, String> namesMap = new HashMap<>();
        for (int i = 0; i < 8; i++){
            namesMap.put(i+"lastName", "firstName"+i+1);
        }
        namesMap.put("lastName", "firstNameSame");
        namesMap.put("lastName1", "firstNameSame");
        return namesMap;
    }

    public static void removeFirstNameDuplicates(Map<String, String> map) {

        HashMap<String, String> mapCopy = new HashMap<>(map);
        Iterator<Map.Entry<String,String>> iteratorForFirstName = mapCopy.entrySet().iterator();

        while (iteratorForFirstName.hasNext())
        {
           Map.Entry<String, String> firstMapPair = iteratorForFirstName.next();
           String firstPairValue = firstMapPair.getValue();
           int count = Collections.frequency(map.values(), firstPairValue);

           if (count > 1)
           {
             removeItemFromMapByValue(map, firstPairValue);
             count = 1;
           }
        }
    }

    public static void removeItemFromMapByValue(Map<String, String> map, String value) {
        HashMap<String, String> copy = new HashMap<String, String>(map);
        for (Map.Entry<String, String> pair : copy.entrySet()) {
            if (pair.getValue().equals(value))
                map.remove(pair.getKey());
        }
    }

    public static void main(String[] args) {
       System.out.println(createMap());
        removeFirstNameDuplicates(createMap());

Andrei

Level 41

5 November 2020, 14:00

I don't know it if is ivisible but there is a line 54 which is a duplicate of line 52, to reprint createMap().

Misiu

Level 41 , Gdansk, Poland

5 November 2020, 14:07

count > 1 Right. Count = 1 is not to remove, there is no repeating.

Andrei

Level 41

5 November 2020, 14:33

Sorry but I'm not understanding what you are saying. Are you suggesting I should remove "count = 1;" ?

Misiu

Level 41 , Gdansk, Poland

5 November 2020, 14:51

All is allright. I,ve just pointed (and agree with you): count must be > 1, must be repeated FirstNames. Oh, in previous post I should write: if count = 1 there is nothing to remove.