Leetcode 每日一题C 语言版 -- 80 remove duplicates from sorted array

Leetcode 每日一题C 语言版 – 80 remove duplicates from sorted array

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问题描述

https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/description/?envType=study-plan-v2&envId=top-interview-150

第26题的升级版，同样思想，难度提升为mid.
点击回到26题解

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

解法一

与第26题稍有不同，需要保留两个相同的数字，因此在其基础上，增加一个dup_num.

#define MAX_DUP_NUM (2)

int removeDuplicates(int* nums, int numsSize) {
    int slow = 0, fast = 1;
    int dup_num = 0;

    if (numsSize <= 1)
        return numsSize;

    while (fast < numsSize) {
        if (nums[slow] != nums[fast]) {
            nums[++slow] = nums[fast];
            dup_num = 0;
        } else {
            dup_num++;
            if (dup_num < MAX_DUP_NUM)
                nums[++slow] = nums[fast];
        }
        fast++;
    }
    return ++slow;
}