27. Remove Element
题目描述
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
numssuch that the firstkelements ofnumscontain the elements which are not equal toval. The remaining elements ofnumsare not important as well as the size ofnums. - Return
k.
中文释义
给定一个整数数组 nums 和一个整数 val,就地移除 nums 中所有等于 val 的元素。元素的顺序可以改变。然后返回 nums 中不等于 val 的元素数量。
考虑不等于 val 的 nums 元素数量为 k,为了通过验证,你需要做以下事情:
- 修改数组
nums,使得nums的前k个元素包含不等于val的元素。nums的其余元素不重要,同样nums的大小也不重要。 - 返回
k。
示例
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).
约束条件
0 <= nums.length <= 1000 <= nums[i] <= 500 <= val <= 100
解题思路
方法
使用双指针技巧来移除数组中的特定元素。
步骤
-
初始化两个指针:
index(慢指针):用于在数组中构建不包含特定值的新数组。i(快指针):用于遍历原数组。
-
遍历数组:
- 遍历数组时,使用快指针
i来检查每个元素。 - 如果当前元素
nums[i]不等于要移除的值val,则将其复制到慢指针index的当前位置,并递增index。
- 遍历数组时,使用快指针
-
更新数组长度:
- 遍历完成后,
index + 1就是新数组的长度,即不包含值val的元素数量。
- 遍历完成后,
代码实现
cpp
class Solution {
public:
int removeElement(vector<int>& nums, int val) {
// 在数组中原地移除元素值为val的元素
// 双指针法
int index = -1;
for (int i = 0; i < nums.size(); i++) {
if (nums[i] != val) {
nums[++index] = nums[i];
}
}
return index + 1;
}
};