Remove Duplicates from Sorted Array II — LeetCode 80 Python Solution

The problem

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.

Example

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];
}

Python solution

class Solution:
    def removeDuplicates(self, nums: List[int]) -> int:
        k = 0
        for x in nums:
            if k < 2 or x != nums[k - 2]:
                nums[k] = x
                k += 1
        return k

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 80. Remove Duplicates from Sorted Array II is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Two Pointers.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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