main.py

# Source: https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii
# Title: Remove Duplicates from Sorted Array II
# Difficulty: Medium
# Author: Mu Yang <http://muyang.pro>

################################################################################################################################
# Given an integer array `nums` sorted in **non-decreasing order**, remove some duplicates **in-place** such that each unique element appears **at most twice**. The **relative order** of the elements should be kept the **same**.
#
# Since it is impossible to change the length of the array in some languages, you must instead have the result be placed in the **first part** of the array `nums`. More formally, if there are `k` elements after removing the duplicates, then the first `k` elements of `nums`should hold the final result. It does not matter what you leave beyond the first`k`elements.
#
# Return `k` after placing the final result in the first `k` slots of `nums`.
#
# Do **not** allocate extra space for another array. You must do this by **modifying the input array in-place** with O(1) extra memory.
#
# **Custom Judge:**
#
# The judge will test your solution with the following code:
#
# ```
# int[] nums = [...]; // Input array
# int[] expectedNums = [...]; // The expected answer with correct length
#
# int k = removeDuplicates(nums); // Calls your implementation
#
# assert k == expectedNums.length;
# for (int i = 0; i < k; i++) {
#     assert nums[i] == expectedNums[i];
# }
# ```
#
# If all assertions pass, then your solution will be **accepted**.
#
# **Example 1:**
#
# ```
# Input: nums = [1,1,1,2,2,3]
# Output: 5, nums = [1,1,2,2,3,_]
# Explanation: Your function should return k = 5, with the first five elements of nums being 1, 1, 2, 2 and 3 respectively.
# It does not matter what you leave beyond the returned k (hence they are underscores).
# ```
#
# **Example 2:**
#
# ```
# Input: nums = [0,0,1,1,1,1,2,3,3]
# Output: 7, nums = [0,0,1,1,2,3,3,_,_]
# Explanation: Your function should return k = 7, with the first seven elements of nums being 0, 0, 1, 1, 2, 3 and 3 respectively.
# It does not matter what you leave beyond the returned k (hence they are underscores).
# ```
#
# **Constraints:**
#
# - `1 <= nums.length <= 3 * 10^4`
# - `-10^4 <= nums[i] <= 10^4`
# - `nums` is sorted in **non-decreasing** order.
#
################################################################################################################################


from typing import List


class Solution:
    def removeDuplicates(self, nums: List[int]) -> int:
        dstIdx = 0
        prev1 = None
        prev2 = None
        for curr in nums:
            if curr == prev1 and curr == prev2:
                continue
            nums[dstIdx] = curr
            dstIdx += 1
            prev2, prev1 = prev1, curr

        return dstIdx