Remove Duplicates from Sorted Array II

Author: fishercoder1534

README.md

@@ -191,6 +191,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |89|[Gray Code](https://leetcode.com/problems/gray-code/)|[Solution](../../blob/master/src/stevesun/algorithms/GrayCode.java)|O(n) |O(1)|Medium|Bit Manipulation
 |86|[Partition List](https://leetcode.com/problems/partition-list/)|[Solution](../../blob/master/src/stevesun/algorithms/PartitionList.java)|O(?) |O(?)|Medium|
 |85|[Maximal Rectangle](https://leetcode.com/problems/maximal-rectangle/)|[Solution](../../blob/master/src/stevesun/algorithms/MaximalRectangle.java)|O(m*n) |O(n)|Hard|DP
+|80|[Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)|[Solution](../../blob/master/src/stevesun/algorithms/RemoveDuplicatesfromSortedArrayII.java)|O(n) |O(n)|Medium|
 |79|[Word Search](https://leetcode.com/problems/word-search/)|[Solution](../../blob/master/src/stevesun/algorithms/WordSearch.java)|O(m*n*l) ? |O(m*n)|Medium|Backtracking/DFS
 |78|[Subsets](https://leetcode.com/problems/subsets/)|[Solution](../../blob/master/src/stevesun/algorithms/Subsets.java)|O(n^2) ? |O(1)|Medium|Backtracking
 |76|[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)|[Solution](../../blob/master/src/stevesun/algorithms/MinimumWindowSubstring.java)|O(n)|O(k)|Hard|Two Pointers

src/stevesun/algorithms/RemoveDuplicatesfromSortedArrayII.java

@@ -0,0 +1,48 @@
+package stevesun.algorithms;
+
+import java.util.ArrayList;
+
+/**
+ * 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.
+ */
+public class RemoveDuplicatesfromSortedArrayII {
+
+    public int removeDuplicates(int[] nums) {
+        int counter = 0;
+        int len = nums.length;
+        if (len == 0) {
+            return 0;
+        }
+        if (len == 1) {
+            return 1;
+        }
+        if (len == 2) {
+            return 2;
+        }
+
+        ArrayList<Integer> a = new ArrayList();
+        a.add(nums[0]);
+        a.add(nums[1]);
+        for (int i = 2; i < len; i++) {
+            if (nums[i] != nums[i - 1]) {
+                a.add(nums[i]);
+            } else if (nums[i] != nums[i - 2]) {
+                a.add(nums[i]);
+            }
+        }
+
+        counter = a.size();
+        for (int i = 0; i < counter; i++) {
+            nums[i] = a.get(i);
+        }
+
+        return counter;
+    }
+
+}