CODEWITHSUNDEEP
java
Betim
Betim

Reputation: 13

How to determine, whether an integer array has duplicate elements or not?

I was asked to write a code, which indicates, whether an integer array has duplicate elements or not. This is what I have so far:

int[] input = {1, 2, 3, 4, 1};
boolean hasDuplicates = false;

for (int i = 0; i < input.length; i++) {
    for (int j = i + 1; j < input.length; j++) {
        if (input[i] != input[j]) {
            hasDuplicates = false;
        } else if (input[i] == input[j]) {
            hasDuplicates = true;
        }
    }
}

However, this code does not work as it was intended to be, because hasDuplicates is always false.

Upvotes: 1

Views: 787

Answers (5)

k314159
k314159

Reputation: 11080

Using Java 8 Streams, stopping on the first found duplicate, a one-liner:

int[] input = {1, 2, 3, 4, 1};
boolean hasDuplicates = !(Arrays.stream(input).allMatch(new HashSet<>()::add))

Upvotes: 0

vh1ne
vh1ne

Reputation: 347

Java 8+ makes life easier. here you go

    int[] input = {1, 2, 3, 4, 1};
    boolean hasDuplicates = false;
    if(Arrays.stream(input).distinct().count() != input.length)
        hasDuplicates=true;
    System.out.println(hasDuplicates);

Upvotes: 1

RAZ_Muh_Taz
RAZ_Muh_Taz

Reputation: 4089

You can also iterate over the array once if you use a HashSet. If the add() returns false then we know we have seen that number before.

int[] input = {1, 2, 3, 4, 1};
boolean hasDuplicates = false;
HashSet<Integer> duplicateSet = new HashSet<>();

for (int i = 0; i < input.length; i++) {
    if(!duplicateSet.add(Integer.valueOf(input[i])))
    {
        hasDuplicates = true;
        break;
    }
}

return hasDuplicates;

Upvotes: 3

HiddenHopes
HiddenHopes

Reputation: 63

You can take the benefit of Set data-structure as well:

int[] input = {1, 2, 3, 4, 1};
boolean hasDuplicates = false;
    
Set<Integer> set = new HashSet<>(input.length);

for (int i : input) {
   if (set.add(i)) {
       hasDuplicates = false;
   }
   else {
      hasDuplicates = true;
      break;
   }
}

Set add(E e) returns true if this set did not already contain the specified element.

In a short way:

int[] input = {1, 2, 3, 4, 1};
boolean hasDuplicates = false;
        
Set<Integer> set = new HashSet<>(input.length);

for (int i : input) {
      if (!set.add(i)) {
           hasDuplicates = true;
           break;
     }
}

Upvotes: 1

azro
azro

Reputation: 54148

Once you have decided that the array hasDuplicates, you may never change that; you can't make disappear the duplicate after. Also use break the loop, at the moment hasDuplicates becomes true

int[] input = {1, 2, 3, 4, 1};
boolean hasDuplicates = false;

for (int i = 0; i < input.length; i++) {
    for (int j = i + 1; j < input.length; j++) {
        if (input[i] == input[j]) {
            hasDuplicates = true;
            break;
        }
    }
    if (hasDuplicates)
        break;
}

Even easier in a method, directly use return

static boolean hasDup(int[] input) {
    for (int i = 0; i < input.length; i++)
        for (int j = i + 1; j < input.length; j++)
            if (input[i] == input[j]) 
                return true;
    return false;
}

Upvotes: 3

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