Unique Element Among Triples

Given an integer array where every element appears exactly three times except for one element that appears only once, find that unique element. Solve it in linear time with constant extra space.

Examples
Input: [2,2,3,2]
Output: 3
Hints

Unique Element Among Triples

Given an integer array where every element appears exactly three times except for one element that appears only once, find that unique element. Solve it in linear time with constant extra space.