27. Remove Element(easy)-优快云博客

本文链接：https://blog.youkuaiyun.com/SourDumplings/article/details/86529258

本文详细解析了LeetCode上的一道经典题目——移除元素。通过C++和Java两种语言实现，展示了如何在不使用额外空间的情况下，从数组中移除指定值的所有实例，并返回新的长度。代码简洁高效，适用于面试准备和技术提升。

Easy

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Given an array nums and a value val, remove all instances of that value in-place and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

The order of elements can be changed. It doesn't matter what you leave beyond the new length.

Example 1:

Given nums = [3,2,2,3], val = 3,

Your function should return length = 2, with the first two elements of nums being 2.

It doesn't matter what you leave beyond the returned length.

Example 2:

Given nums = [0,1,2,2,3,0,4,2], val = 2,

Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4.

Note that the order of those five elements can be arbitrary.

It doesn't matter what values are set beyond the returned length.

Clarification:

Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.

Internally you can think of this:

// nums is passed in by reference. (i.e., without making a copy)

int len = removeElement(nums, val);

// any modification to nums in your function would be known by the caller.

// using the length returned by your function, it prints the first len elements.

for (int i = 0; i < len; i++) {

    print(nums[i]);

C++：

/*
 @Date    : 2019-01-15 19:59:41
 @Author  : 酸饺子 (changzheng300@foxmail.com)
 @Link    : https://github.com/SourDumplings
 @Version : $Id$
*/

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

class Solution
{
public:
    int removeElement(vector<int>& nums, int val)
    {
        if (nums.empty())
        {
            return 0;
        }
        for (auto it = nums.begin(); it != nums.end();)
        {
            if (*it == val)
            {
                it = nums.erase(it);
            }
            else
                ++it;
        }
        return nums.size();
    }
};

Java：

/**
 * @Date    : 2019-01-15 20:15:20
 * @Author  : 酸饺子 (changzheng300@foxmail.com)
 * @Link    : https://github.com/SourDumplings
 * @Version : $Id$
 *
 * https://leetcode.com/problems/remove-element/submissions/
*/

class Solution
{
    public int removeElement(int[] nums, int val)
    {
        if (nums.length == 0)
        {
            return 0;
        }
        int back = nums.length - 1;
        for (int i = 0; i <= back;)
        {
            if (nums[i] == val)
            {
                nums[i] = nums[back];
                --back;
            }
            else
                ++i;
        }
        return back + 1;
    }
}