remove duplicates in sorted array II: keep two copies only, but remove others.

remove_duplicates_in_sorted_array_II.cpp

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if (n <= 2)
            return n;
        int slow = 0;
        int fast = slow + 1;
        while (fast < n) {
            // keep two copies
            if (A[fast] == A[slow] ) {
                //Note: must copy to slow+1, since it may hold OLD values.
                A[slow+1] = A[fast];
                slow ++;
                fast ++;
            }
            while (fast < n && A[fast] == A[slow])
                fast ++;
            if (fast >= n)
                break;
            //now A[fast] != A[slow], copy and set it as new base element
            A[slow+1]  = A[fast];
            slow = slow + 1;
            fast ++;
        }
        return slow + 1;
    }
};