InterviewBit Problems   Find Duplicate in Array : Unsolved

About the Find Duplicate in Array : Unsolved category (1)
Just sort the array and then just compare ith and ith +1 (2)
The test Cases are too poor (1)
Interesting Solution using fast and slow pointer (6)
Do maps take more memory than arrays? (1)
Can someone tell me what is wrong with my solution? (3)
Simple Solution O(N) using Array to count the Duplicate (2)
Easy 5 line solution - O(N) (2)
Trash IDE and testcases -- It is giving wrong answer for O(1) space when the solution is actually giving correct answer on other IDEs (2)
My code gives Runtime Error, while running correctly on my local machine (1)
XOR Solution wrong? (1)
Easy 5 Line solution (2)
Doubt regarding traversal (2)
Python 3 Solution [Using Counter] (1)
Memory limit exceeded is exceeded for map, can you guys please help me correct it? (1)
Point for Easy Solution using HashSet in Java (1)
I dont know how to solve it in less than O(n) space. help please! (7)
Duplicate in array in o(1) space (1)
Can't figure out my mistake (3)
Wrong solution given. Please change it according to problem description (1)
Just ignore it outout -1 (1)
O(n) solution giving wrong ans! (1)
Worng answer in fastest and lightweight solution (2)
Trash Question - Do not waste time (2)
Why is my solution exceeding memory limit even though it'll take O(n) space in worst case? (1)
Isnt the solution posted is wrong? (1)
Pls help,error is undefined reference to `Solution::repeatedNumber(std::vector<int, std::allocator<int> > const&)' collect2: error: ld returned 1 exit status (2)
O(n) TC, O(1) space (2)
Xor Solution Giving Wrong Answer , But get Accepted (1)
Wrong Expected O/P! (1)