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  1. Lonely Integer
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Lonely Integer

  • juanp766
     + 0 comments

    Java using two hash sets which operations are O(1), therefore it is only needed to iterate whole array once.

    public static int lonelyinteger(List<Integer> arr) {
        HashSet<Integer> set = new HashSet<>();
        HashSet<Integer> uniqueSet = new HashSet<>();
        
        Integer unique = arr.get(0);
        Integer lastUnique = arr.get(0);
        
        for(Integer element: arr){
            if(!set.contains(element)){
                set.add(element);
                uniqueSet.add(element);
            }else{
                uniqueSet.remove(element);
            }
        }
        
        return uniqueSet.stream().findFirst().get();
    }