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# 27 Remove Element

## 27. Remove Element

## 1. Question

Given an array and a value, remove all instances of that value [**in-place**](https://en.wikipedia.org/wiki/In-place_algorithm) and return the new length.

Do not allocate extra space for another array, you must do this by **modifying the input array** [**in-place**](https://en.wikipedia.org/wiki/In-place_algorithm)with O(1) extra memory.

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

**Example:**

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

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

## 2. Implementation

```java
public class Solution {
    public int removeElement(int[] nums, int val) {
        if (nums == null || nums.length == 0) {
            return 0;
        }

        int index = 0;
        for (int num : nums) {
            if (num != val) {
                nums[index++] = num;
            }
        }
        return index;
    }
}
```

## 3. Time & Space Complexity

时间复杂度O(n), 空间复杂度O(1)