Given a list of integers integer_list, where every element appears exactly three times except for one element that appears exactly once, return the element that appears only once. The solution must run in linear time and use constant extra space.
Example 1
Input: [7,7,7,4,4,4,8]
Output: 8
Explanation: 8 appears once, all others appear three times.
Example 2
Input: [-5,-5,-5,12,12,12,0]
Output: 0
Explanation: 0 appears once, all others appear three times.
Example 3
Input: [100,100,100,200,200,200,300]
Output: 300
Explanation: 300 appears once, all others appear three times.
Constraints
Case 1
Input: [9,9,9,11,11,11,15]
Expected: 15
Case 2
Input: [23,23,23,42,42,42,17]
Expected: 17
Case 3
Input: [-1,-1,-1,-2,-2,-2,5]
Expected: 5
Case 4
Input: [0,0,0,1,1,1,2]
Expected: 2