write a method to return the duplicate in a integer array

Question

Anonym · Accepted Answer

int dupElement(int[] array){
      for(int i=0; i < array.length;i++){
         for(int j=0; j < array.length; j++){
        if(array[i] == array[j])
            return array[i];
}     
}
}

Gave another solution by adding boolean array which can return value with order of O(n) and O(1)

Craig · Answer

You would always return a false positive in your double for loop because you'd compare the first element with itself and suggest its a duplicate. Using a boolean array could work, but depending on how you set it, it may be wasting space.

The dictionary is a better solution, but it still is wasting space. There is no need to keep keys and values in the instance. The best solution is to use a set to keep track of everything you've seen thus far.

Example:

Set found = new HashSet();
for (int i = 0; i < array.length; i++) {
    if (found.contains(array[i])
        return array[i];
    found.add(array[i]);
}
// denotes no duplicates
return -1;

David · Answer

This doesn't seem right to me. This solution is just telling you if the item at position i is equal to item at position j which is always true. 

My thinking is to add each value you find to a dictionary and when going to the next one, check if it exists. If it does then it is a duplicate so return that.

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