Notes:

1. Still need to pay attention that return start since start represents current index to place next int.

2. define start outside of loop.

class Solution {    public int removeDuplicates(int[] nums) {        if (nums.length < 2) {            return nums.length;        }                int prev = nums[0];        int start = 1;        for (int runner = 1; runner < nums.length; runner++) {            if (prev != nums[runner]) {                nums[start++] = nums[runner];                prev = nums[runner];            }        }        return start;    }}