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# Element that appears once

Difficulty: EASY Contributed By
Arshit Babariya
Avg. time to solve
15 min
Success Rate
85%

Problem Statement
Suggest Edit

#### You are given an arbitrary array ‘arr’ consisting of N non-negative integers, where every element appears thrice except one. You need to find the element that appears only once.

##### Input Format:
``````The first line of the input contains a single integer T, representing the number of test cases.

The first line of each test case consists of a single integer N, representing the number of elements in the given array.

The second line of each test case contains N space-separated integers, denoting the elements of the array.
``````
##### Output Format:
``````For each test case, print a single integer representing the element that appears only once in the array.
``````
##### Note:
``````You do not need to print anything. It has already been taken care of. Just implement the given function.
``````
##### Constraints:
``````1 <= T <= 100
4 <= N <= 10^4
0 <= arr[i] < 10^9
Time Limit: 1sec
``````
``````Try to solve this problem in O(N) time and O(1) space complexity.
``````
##### Sample Input 1:
``````1
4
1 2 1 1
``````
##### Sample Output 1:
``````2
``````
##### Explanation For Sample Input 1:
``````Clearly, the 2 appears once while 1 appears thrice. Hence, 2 is the output.
``````
##### Sample Input 2:
``````1
7
1 3 3 3 1 1 4
``````
##### Sample Output 2:
``````4
``````   Console