LeetCode-27. Remove Element | 移除元素

题目

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.

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 a 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]);
}

Example 1:

Input: nums = [3,2,2,3], val = 3
Output: 2, nums = [2,2]
Explanation: 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. For example if you return 2 with nums = [2,2,3,3] or nums = [2,2,0,0], your answer will be accepted.
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 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.


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

题解

难度为简单。

特别注意不要使用额外的数组空间，你必须仅使用 O(1) 额外空间并原地修改输入数组。

解法一：双指针法

//Go
func removeElement(nums []int, val int) int {
    //双指针法
    i := 0
    for j := 0;j < len(nums);j++ {  //遍历nums数组
        if nums[j] != val {  //如果nums下标 j 对应的元素不等于 val
            nums[i] = nums[j]
            i++
        }
    }

    return i
}

执行结果：

leetcode-cn：
执行用时：0 ms, 在所有 Go 提交中击败了100.00%的用户
内存消耗：2.1 MB, 在所有 Go 提交中击败了99.85%的用户

leetcode：
Runtime: 0 ms, faster than 100.00% of Go online submissions for Remove Element.
Memory Usage: 2.1 MB, less than 17.08% of Go online submissions for Remove Element.