InterviewBit Problems   Single Number II : Unsolved

About the Single Number II : Unsolved category (1)
Please clear my doubt (1)
FInd the error (Quite hard to spot) (2)
Isn't this O(n) time complexity? (3)
Sort(A.begin(),A.end()) gives error why? (6)
TC : O(N) & SC : O(1) with easy & understandable code! (3)
Accepted Java solution without using Bit Operations (2)
Extra space allocation (5)
Explanation for the hint (3)
Why Bit? Sorting will also do it in O(32N) (2)
Expected Output and WA Explaination (2)
Partiial solution (1)
Question does not work on negative integers (1)
Shows time limit exceeds (2)
Can the number appear more than thrice? (3)
Find that single one = find that one element or find that element that appears o (2)