80. Remove Duplicates from Sorted Array II

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.

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:

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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.

https://leetcode.cn/problems/remove-duplicates-from-sorted-array-ii/

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 * 10⁴
• -104 <= nums[i] <= 10⁴
• nums is sorted in non-decreasing order.

Test Cases

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class Solution:
    def removeDuplicates(self, nums: List[int]) -> int:

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import pytest

from solution import Solution


@pytest.mark.parametrize('nums, expected, expectedNums', [
    ([1,1,1,2,2,3], 5, [1,1,2,2,3]),
    ([0,0,1,1,1,1,2,3,3], 7, [0,0,1,1,2,3,3]),
])
@pytest.mark.parametrize('sol', [Solution()])
def test_solution(sol, nums, expected, expectedNums):
    nums = nums.copy()
    assert sol.removeDuplicates(nums) == expected
    assert nums[:expected] == expectedNums

Thoughts

26. Remove Duplicates from Sorted Array 的进阶版，每个数字最多可以保留两个。

直接搬 problem 26 的代码，把其中的 1 改成 2 即可。

时间复杂度 O(n)，空间复杂度 O(1)。

Code

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class Solution:
    def removeDuplicates(self, nums: list[int]) -> int:
        n = len(nums)
        l = r = 2
        while r < n:
            if nums[r] != nums[l - 2]:
                nums[l] = nums[r]
                l += 1
            r += 1

        return l

参考资料

• 本文引用

  • 26. Remove Duplicates from Sorted Array

许可协议

本文除了题目描述（Problem）部分之外，其他内容由 Calf 原创，采用 CC BY-NC-SA 4.0 许可协议，转载请注明出处。

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