题目

地址

https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/

内容

Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums.

Consider the number of unique elements of nums to be k, to get accepted, you need to do the following things:

• Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums.
• Return k.

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 = [1,1,2]
Output: 2, nums = [1,2,_]
Explanation: Your function should return k = 2, with the first two elements of nums being 1 and 2 respectively.
It does not matter what you leave beyond the returned k (hence they are underscores).

Example 2:

Input: nums = [0,0,1,1,1,2,2,3,3,4]
Output: 5, nums = [0,1,2,3,4,,,,,_]
Explanation: Your function should return k = 5, with the first five elements of nums being 0, 1, 2, 3, and 4 respectively.
It does not matter what you leave beyond the returned k (hence they are underscores).

Constraints:

• 1 <= nums.length <= 3 * 10⁴
• -100 <= nums[i] <= 100
• nums is sorted in non-decreasing order.

解题

这题要求在一个包含重复数字的升序数组中，找到所有出现的数字（剔除重复的部分），并将它们放到数组的头部。比如 [0,0,1,1,1,2,2,3,3,4]中有大量重复数字，但是只出现了0、1、2、3、4这五个数。我们要将这五个数字放到数组头部，剩下的位放什么数字无所谓。
题中提到数组是有序数组，这意味着我们在找重复数字时只要用数字和前面的数字做对比即可。其次对于结果数组，不需要考虑未被改变的空间的值。那么我们就只用找到出现的数字，并递增索引号来存储它们即可。

#include <vector>
using namespace std;class Solution {
public:int removeDuplicates(vector<int>& nums) {if (nums.empty()) return 0;int uniqueIndex = 1;for (int i = 1; i < nums.size(); i++) {if (nums[i] != nums[uniqueIndex - 1]) {nums[uniqueIndex++] = nums[i];}}return uniqueIndex;}
};

代码地址

https://github.com/f304646673/leetcode/tree/main/26-Remove-Duplicates-from-Sorted-Array