题目

地址

https://leetcode.com/problems/remove-element/description/

内容

Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val.

Consider the number of elements in nums which are not equal to val 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 elements which are not equal to val. 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 val = …; // Value to remove
int[] expectedNums = […]; // The expected answer with correct length.
// It is sorted with no values equaling val.
int k = removeElement(nums, val); // Calls your implementation
assert k == expectedNums.length;
sort(nums, 0, k); // Sort the first k elements of nums
for (int i = 0; i < actualLength; i++) {
assert nums[i] == expectedNums[i];
}

If all assertions pass, then your solution will be accepted.

Example 1:

Input: nums = [3,2,2,3], val = 3
Output: 2, nums = [2,2,,]
Explanation: Your function should return k = 2, with the first two elements of nums being 2.
It does not matter what you leave beyond the returned k (hence they are underscores).

Example 2:

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

Constraints:

• 0 <= nums.length <= 100
• 0 <= nums[i] <= 50
• 0 <= val <= 100

解题

这题就是要将数组中某个元素删除，空出来的位置由后续不是该值的元素来补位。返回删除后剩下的有效元素个数。对于无效位置，其值不做考察。
这题的解法也很简单，遍历一次，剔除待删除元素，然后将后续的元素向前移动。

#include <vector>
using namespace std;

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int index = 0;
        for (int v : nums) {
            if (v != val) {
                nums[index++] = v;
            }
        }
        return index;
    }
};

代码地址

https://github.com/f304646673/leetcode/tree/main/27-Remove-Element