LeetCode 268. Missing Number

Problem:

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?

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

Solution:

O(n) time, O(1) space

public class Solution {
    public int missingNumber(int[] nums) {
        int sum = 0;
        for (int i = 1; i <= nums.length; i++) sum += i;
        for (int i = 0; i < nums.length; i++) sum -= nums[i];
        return sum;
    }
}