80. Remove Duplicates from Sorted Array II (https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/): Given a sorted array nums, remove the duplicates in-place such that duplicates appeared at most twice and return the new length. Do not allocate extra space for another array, you must do this by modifying the input array in-place …

80. Remove Duplicates from Sorted Array II (#1 Two pointer).java

// Two pointer: read/write pointers (slow/fast pointers)
// Time: O(n), 0ms
// Space: O(1), 37.2mb
class Solution {
    public int removeDuplicates(int[] nums) {
        // Corner cases
        if(nums.length < 3) return nums.length;
        
        int w = 2, r = 2;
        // Read pointer moves every loop
        for(; r < nums.length; r++) {
            if(nums[r] > nums[w - 2] ) {
                // !!: Write when we won't make 3 dups in a row
                nums[w++] = nums[r];
            }
        }
        
        return w;
    }
}

80. Remove Duplicates from Sorted Array II (#1.2 Two pointer).java

// Two pointer: read/write pointers (slow/fast pointers)
// Time: O(n), 0ms
// Space: O(1), 37.3mb
class Solution {
    public int removeDuplicates(int[] nums) {
        int i = 0;  //i is slow pointer
        for (int n : nums)  //n is fast pointer
            if (i < 2 || n > nums[i-2])  //When slow is not the third in a row
                nums[i++] = n;  //Assign fast to slow
        return i;
    }
}