remove duplicates in sorted array. Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this in place with constant memory. For example, Given input array A = [1,1,2], Your function should return length = 2, and A is now …

remove_duplicates_in_sorted_array.cpp

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if (n <= 0)   //necessary, since slow is baed on 0 as in next
            return n;
        //two pointers, one slow, one fast
        // sweep fast if A[fast ] == A[slow]
        //      if new element found, keep it, set as new base element
        int moveToLeft = 0;
        int slow = 0;
        int fast = slow + 1;
        while (fast < n) {
            //skip same values with slow
            while (fast < n && A[fast] == A[slow] )
                fast ++;
            if (fast >= n)
                break;
            //now A[fast] != A[slow], copy to A[slow+1]
            A[slow+1] = A[fast];
            //new base as in A[slow+1]
            slow = slow + 1;
            fast ++;    //fast should be always faster than slow
        }
        return slow + 1;
    }
};