## Description

https://leetcode.com/problems/missing-number/

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

**Note**:

Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

## Explanation

use a hashmap to help check which number is missing

## Python Solution

```
class Solution:
def missingNumber(self, nums: List[int]) -> int:
n = len(nums)
visited = set()
for num in nums:
visited.add(num)
for i in range(0, n + 1):
if i not in visited:
return i
```

- Time complexity: O(N).
- Space complexity: O(1).

## One Thought to “LeetCode 268. Missing Number”