27.md

27. Remove Element

Description

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.

Thinking Process

1. Scan from the beginning of the array, whenever we saw the target, swap it with nums[len - 1], then decrease len by 1
2. Return len as the new length of the array

Code

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

Complexity

1. Space complexity is O(1)
2. Time complexity is O(n)