public class Solution {

// Complete the findLonely function below.
static int findLonely(List<Integer> arr) {
    int num=0;
   for(int i:arr){
       num=num^i;
   }return num;

}

Brute force C++ Code || Bit Manipulation

int findLonely(vector<int> arr) {
    int ans = 0;
    for(int i=0;i<arr.size();i++)
    {
        ans = ans ^ arr[i];
    }
    return ans;
}

Tiny Ruby solution:

def find_lonely(arr)
  arr.inject(&:^)
end

_n = gets.to_i
arr = gets.split.map(&:to_i)
puts find_lonely(arr)

Another way of doing the code: def findLonely(arr): array = list(set(arr)) for i in range(len(array)): if arr.count(array[i]) !=2: return array[i]

Another way of doing the code: def findLonely(arr): array = list(set(arr)) for i in range(len(array)): if arr.count(array[i]) !=2: return array[i]