Find the Missing Value in a Complete Integer Range
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
# Find the Missing Value in a Complete Integer Range
An array `nums` contains `n` distinct integers chosen from the inclusive range `[0, n]`. Exactly one value in that range is absent. Return it.
### Function
`int missingNumber(vector<int>& nums)`
### Example 1
```text
Input: nums = [4,0,2,1]
Output: 3
```
There are four entries, so the complete range is `0` through `4`. Only `3` is missing.
### Example 2
```text
Input: nums = [1]
Output: 0
```
### Constraints
- `n == nums.length`.
- `1 <= n <= 10000`.
- `0 <= nums[i] <= n`.
- All entries are distinct.
### Clarifications
The range includes both `0` and `n`; neither is guaranteed to appear. The input need not be sorted. Return the absent value, not an array index.
### What a Strong Answer Covers
- How the complete expected range relates to the actual entries.
- Why the distinctness and range guarantees identify exactly one answer.
- Missing boundary values and an input of length one.
- Time and auxiliary-space requirements.
### Follow-up Questions
Can you solve the problem in `O(n)` time with `O(1)` extra space?
Overview: Practice identifying the sole missing value from an inclusive integer range. Preserve the distinctness guarantee, handle either missing endpoint, and explain time and storage costs.