Missing Number - LeetCode

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

Example 1:

Input: [3,0,1]
Output: 2

Example 2:

Input: [9,6,4,2,3,5,7,0,1]
Output: 8

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

Java Solution :

class Solution {
    public int missingNumber(int[] nums) {
        if(nums == null || nums.length < 1)
            return 0;
        Arrays.sort(nums);
        int n = nums[nums.length-1];
        int sum = (n*(n+1))/2;
        int result = 0;
        for(int i=0;i<nums.length;i++)
            result+=nums[i];
        if(result == sum && nums[0]==0)
            return nums[nums.length-1]+1;
        return sum-result;
    }
}