[Leetcode] Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

For example,
Given nums = [0, 1, 3] return 2.

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

public class Solution {
    private void swap(int[] nums, int pos1, int pos2) {
        int tmp = nums[pos1];
        nums[pos1] = nums[pos2];
        nums[pos2] = tmp;
    }
    public int missingNumber(int[] nums) {
        int i = 0;
        while(i < nums.length) {
            if(i == nums[i] || nums[i] >= nums.length) {
                i++;
            }
            else {
                swap(nums, i, nums[i]);
            }
        }
        
        for(i = 0; i < nums.length; i++) {
            if(i != nums[i]) {
                return i;
            }
        }
        return nums.length;
    }
}

Better solution by sum and subtraction