Finding the unique number in an array

Given an array of numbers which contains all the numbers in pairs expect one element. We have to find that unique element.

For example in the array [7,3,8,1,3,4,7,1,8] 4 is the unique element and all the remaining elements occur in pairs.

This is actually a specific case of more generic problem discussed in the my previous post. 

http://comproguide.blogspot.in/2013/06/finding-element-occurring-odd-number-of.html

please refer to the above post for complete solution.