LeetCode - Missing Number

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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

class Solution {
    public int missingNumber(int[] nums) {
        if(nums == null){
            return -1;
        }
        int len = nums.length;
        int total = (0+len)*(len+1)/2;
        int sum=0;
        for(int i=0; i<nums.length; i++){
            sum = sum + nums[i];
        }
        return total - sum;
        
    }
}