Java Array, Finding Duplicates

user_458960 0
Viewed 261926

I have an array, and am looking for duplicates.

duplicates = false;
for(j = 0; j < zipcodeList.length; j++){
    for(k = 0; k < zipcodeList.length; k++){
        if (zipcodeList[k] == zipcodeList[j]){
            duplicates = true;
        }
    }
}

However, this code doesnt work when there are no duplicates. Whys that?

arrays java
16 Answers
public static ArrayList<Integer> duplicate(final int[] zipcodelist) {

    HashSet<Integer> hs = new HashSet<>();
    ArrayList<Integer> al = new ArrayList<>();
    for(int element: zipcodelist) {
        if(hs.add(element)==false) {
            al.add(element);
        }   
    }
    return al;
}
user_100684090

This program will print all duplicates value from array.

public static void main(String[] args) {

    int[] array = new int[] { -1, 3, 4, 4,4,3, 9,-1, 5,5,5, 5 };
    
    Arrays.sort(array);

 boolean isMatched = false;
 int lstMatch =-1;
      for(int i = 0; i < array.length; i++) {  
          try {
                if(array[i] == array[i+1]) { 
                    isMatched = true;
                    lstMatch = array[i+1]; 
                }
                else if(isMatched) {
                    System.out.println(lstMatch);
                    isMatched = false;
                    lstMatch = -1;
                }
          }catch(Exception ex) {
              //TODO NA
          }

      }
      if(isMatched) {
          System.out.println(lstMatch);
      }

}

}

user_75921880 
  public static void findDuplicates(List<Integer> list){
    if(list!=null && !list.isEmpty()){
      Set<Integer> uniques = new HashSet<>();
      Set<Integer> duplicates = new HashSet<>();

      for(int i=0;i<list.size();i++){
        if(!uniques.add(list.get(i))){
          duplicates.add(list.get(i));
        }
      }
      System.out.println("Uniques: "+uniques);
      System.out.println("Duplicates: "+duplicates);
    }else{
      System.out.println("LIST IS INVALID");
    }
  }
user_120087350 
public static <T> Set<T> getDuplicates(Collection<T> array) {
    Set<T> duplicateItem = new HashSet<>();
    Iterator<T> it = array.iterator();
    while(it.hasNext()) {
        T object = it.next();
        if (Collections.frequency(array, object) > 1) {
            duplicateItem.add(object);
            it.remove();
        }
    }
    return duplicateItem;
}

// Otherway if you dont need to sort your collection, you can use this way.

public static <T> List<T> getDuplicates(Collection<T> array) {
    List<T> duplicateItem = new ArrayList<>();
    Iterator<T> it = array.iterator();
    while(it.hasNext()) {
        T object = it.next();
        if (Collections.frequency(array, object) > 1) {
            if (Collections.frequency(duplicateItem, object) < 1) {
                duplicateItem.add(object);
            }
            it.remove();
        }
    }
    return duplicateItem;
}
user_161918080
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