27. Remove Element

Given an array and a value, 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 in place with constant memory.

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

Example:
Given input array nums = [3,2,2,3], val = 3

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

Solution:

Set index to 0, which means this index can put a valid number.

Go through the input array.

If the number does not equals to value, it is a valid number and can be put in index.

Put this number in index and increment the index.

The time complexity is O(n) and the space complexity is O(1).



Code:

public class Solution {
    public int removeElement(int[] nums, int val) {
        int i = 0;
        for (int n : nums) {
            if (n != val) {
                nums[i++] = n;
            }
        }
        return i;
    }
}