27. Remove Element

難度: Easy

類型: Linked List

CPP程式下載: 27.cpp

前情題要:

給一個從小到大排序的陣列, 以及一個數 val, 要求把和val數字相同的剔除, 並回傳不為val值的個數, 以及剔除相同值後的陣列。

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

 

思考方式:

1. 其實不必兩個 pointer, 兩個 index 就可以了, 一樣意思。

2. 重複的剔掉後, 後面 array 的值為 don't case, 不必處理。

複雜度思考:

Time Complexity: Worst case: O( N )

Space Complexity: O( x )

結果:

Runtime: 0 ms, Beats: 100%

Memory: 11.72 MB, Beats: 46.82%

Accepted

116 / 116 testcases passed

tendchen

submitted at Nov 10, 2025 21:34

Runtime

0ms

Beats100.00%

Analyze Complexity

Memory

11.72MB

Beats46.82%

Analyze Complexity

Code

C++

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int iSize = nums.size();
        int iInputIndex=0;
        int iOutputIndex=0;

        for (;iInputIndex<iSize;iInputIndex++)
        {
            if (nums.at(iInputIndex)==val)
            {
                continue;
            }
            else
            {
                nums.at(iOutputIndex)=nums.at(iInputIndex);
                iOutputIndex++;
            }
        }
        return iOutputIndex;
    }
};