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# Duplicate In Array

Easy
0/40
Average time to solve is 15m
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## Problem statement

You are given an array â€˜ARRâ€™ of size â€˜Nâ€™ containing each number between 1 and â€˜Nâ€™ - 1 at least once. There is a single integer value that is present in the array twice. Your task is to find the duplicate integer value present in the array.

For example:

``````Consider ARR = [1, 2, 3, 4, 4], the duplicate integer value present in the array is 4. Hence, the answer is 4 in this case.
``````
Note :
``````A duplicate number is always present in the given array.
``````
Detailed explanation ( Input/output format, Notes, Images )
Constraints:
``````1 <=  T  <= 10
2 <=  N <= 10 ^ 5
1 <=  ARR[i]  <= N - 1

Where 'T' denotes the number of test cases, 'N' denotes the number of elements in the array, and 'ARR[i]' denotes the 'i-th' element of the array 'ARR'.

Time limit: 1 sec
``````
##### Sample Input 1:
``````2
5
4 2 1 3 1
7
6 3 1 5 4 3 2
``````
##### Sample Output 1:
``````1
3
``````
##### Explanation of sample input 1:
``````For the first test case,
The duplicate integer value present in the array is 1. Hence, the answer is 1 in this case.

For the second test case,
The duplicate integer value present in the array is 3. Hence, the answer is 3 in this case.
``````
##### Sample Input 2:
``````2
6
5 1 2 3 4 2
9
8 7 2 5 4 7 1 3 6
``````
##### Sample Output 2:
``````2
7
``````

##### Hints:
``````1. Simply calculate the frequency of each value.
2. Try to optimise the above approach by using an array to store the frequencies.
3. Think of a solution using Floydâ€™s cycle finding algorithm.
4. Try to think of a solution based on bitwise XOR.
``````
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