# 80 Remove Duplicates from Sorted Array II – Medium

### Problem:

Follow up for “Remove Duplicates”: What if duplicates are allowed at most twice?

For example, Given sorted array nums = [1,1,1,2,2,3],

Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3. It doesn’t matter what you leave beyond the new length.

### Thoughts:

The most straight forward way is to modify the version I solution, adding a flag to indicate if an element has appeared once.

There could be a better solution that is a little simpler in code, but it has the same running complicity of O(n).

### Solutions:

Modified version I with flag:

``````public class Solution {
public int removeDuplicates(int[] A) {
if (A == null || A.length == 0)
return 0;
int pre = A[0];
boolean flag = false;
int count = 0;
// index for updating
int o = 1;
for (int i = 1; i < A.length; i++) {
int curr = A[i];
if (curr == pre) {
if (!flag) {
flag = true;
A[o++] = curr;
continue;
}
else {
count++;
}
}
else {
pre = curr;
A[o++] = curr;
flag = false;
}
}
return A.length - count;
}
}
``````

Simpler version code with two pointer:

``````public class Solution {
public int removeDuplicates(int[] A) {
if (A.length <= 2)
return A.length;
int prev = 1; // point to previous
int curr = 2; // point to current
while (curr < A.length) {
if (A[curr] == A[prev] && A[curr] == A[prev - 1]) {
curr++;
}
else {
prev++;
A[prev] = A[curr];
curr++;
}
}

return prev + 1;
}
}
``````