How does one remove duplicate elements in place in an array in O(n) in C or C++?

Question

Is there any method to remove the duplicate elements in an array in place in C/C++ in O(n)? Suppose elements are a[5]={1,2,2,3,4} then resulting array should c

Answer 1

If, and only if, the source array is sorted, this can be done in linear time:

std::unique(a, a + 5); //Returns a pointer to the new logical end of a.

Otherwise you'll have to sort first, which is (99.999% of the time) n lg n.