# Missing Number
https://leetcode.com/problems/missing-number/
## Solution 1: Indexing
```python
table = [0] * (len(nums) + 1)
for num in nums:
table[num] = 1
return table.index(0)
```
## Solution 2: Gauss's Formula (Summation)
```python
n = len(nums)
return n * (n + 1) // 2 - sum(nums)
```
## Solution 3: XOR
```python
missing = len(nums)
for i, num in enumerate(nums):
missing ^= i ^ num
return missing
```
Utilizing the fact that `x ^ x = 0`, and `x ^ 0 = x`. The index and number cancels each other. Initialize `missing = len(nums)`, since the index `n` is not iterated.