# 1863. Sum of All Subset XOR Totals

Easy
The XOR total of an array is defined as the bitwise `XOR` of all its elements, or `0` if the array is empty.
• For example, the XOR total of the array `[2,5,6]` is `2 XOR 5 XOR 6 = 1`.
Given an array `nums`, return the sum of all XOR totals for every subset of `nums`.
Note: Subsets with the same elements should be counted multiple times.
An array `a` is a subset of an array `b` if `a` can be obtained from `b` by deleting some (possibly zero) elements of `b`.
Example 1:
Input: nums = [1,3]
Output: 6
Explanation: The 4 subsets of [1,3] are:
- The empty subset has an XOR total of 0.
-  has an XOR total of 1.
-  has an XOR total of 3.
- [1,3] has an XOR total of 1 XOR 3 = 2.
0 + 1 + 3 + 2 = 6
Example 2:
Input: nums = [5,1,6]
Output: 28
Explanation: The 8 subsets of [5,1,6] are:
- The empty subset has an XOR total of 0.
-  has an XOR total of 5.
-  has an XOR total of 1.
-  has an XOR total of 6.
- [5,1] has an XOR total of 5 XOR 1 = 4.
- [5,6] has an XOR total of 5 XOR 6 = 3.
- [1,6] has an XOR total of 1 XOR 6 = 7.
- [5,1,6] has an XOR total of 5 XOR 1 XOR 6 = 2.
0 + 5 + 1 + 6 + 4 + 3 + 7 + 2 = 28
Example 3:
Input: nums = [3,4,5,6,7,8]
Output: 480
Explanation: The sum of all XOR totals for every subset is 480.
Constraints:
• `1 <= nums.length <= 12`
• `1 <= nums[i] <= 20`

### 解題

func subsetXORSum(nums []int) int {
ans := 0
var dfs func(int, int)
dfs = func(index int, xor int) {
if index >= len(nums) { return }
ans += xor ^ nums[index]
dfs(index + 1, xor ^ nums[index])
dfs(index + 1, xor)
}
dfs(0, 0)
return ans
}