[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 int missingNumber(int[] nums) {

int xor = 0, i = 0;
for (i = 0; i < nums.length; i++) {
xor = xor ^ i ^ nums[i];
}

return xor ^ i;
}

public int missingNumber(int[] nums) {
int sum = 0;
for(int i : nums) {
sum += i;
}
int n = nums.length;
int tmp = (n+1)*n/2;
return tmp-sum;
}