Remove Duplicates from Sorted Array II

• Time : $O(n)$
• Space : $O(1)$

int Solution::removeDuplicates(vector<int> &A) {
    int res = 0, l = 2, r = 2, n = A.size();
    if(n < 3) return n;
    while(r < n) {
        if(A[r] != A[l-2]) A[l++] = A[r];
        r++;
    }
    return l;
}

• Time : $O(n^2)$
• Space : $O(1)$

int Solution::removeDuplicates(vector<int> &A) {
    int res = 0, l = 0, r = 0, n = A.size();
    while(l < n) {
        if(l and A[l-1] == A[l]) l++;
        else if(l + 1 < n and A[l] != A[l+1]) l++;
        else {
            r = l + 2;
            while(r < n and A[r] == A[l]) res += 1, r += 1;
            for(int i = l + 2, j = r; j < n; j++,i++) {
                A[i] = A[j];
            }
            n -= (r - (l + 2));
            l += 2;
        }
    }
    return A.size() - res;
}