Length of the Longest Contiguous Subarray Summing to a Target
Company: eBay
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
Given an integer array `nums` and an integer `k`, return the length of the longest contiguous subarray whose elements sum to exactly `k`. If no such subarray exists, return `0`.
### Function Signature
```python
def longest_subarray_with_sum(nums: list[int], k: int) -> int:
```
### Rules
- A subarray is a non-empty contiguous block `nums[i..j]` with `i <= j`.
- Elements may be negative, zero or positive.
- Only the length is returned, so it does not matter which of several longest qualifying subarrays you have in mind.
### Constraints
- `1 <= len(nums) <= 2 * 10^5`
- `-10^4 <= nums[i] <= 10^4`
- `-10^9 <= k <= 10^9`
- Every subarray sum lies within `[-2 * 10^9, 2 * 10^9]`, which fits in a 32-bit signed integer.
### Examples
**Example 1**
```text
Input: nums = [2, -1, 3, 1, -2, 2], k = 3
Output: 5
```
Both `[2, -1, 3, 1, -2]` and `[-1, 3, 1, -2, 2]` sum to 3. The whole array sums to 5, so no subarray of length 6 qualifies.
**Example 2**
```text
Input: nums = [1, 2, 3], k = 7
Output: 0
```
The largest possible sum is 6, so no subarray sums to 7.
**Example 3**
```text
Input: nums = [0, 0, 0], k = 0
Output: 3
```
The whole array sums to 0.
Overview: Given an integer array that may contain negative numbers and a target k, return the length of the longest contiguous subarray whose sum equals k, or 0 when none exists. Tests reasoning about subarray sums with mixed signs and handling large inputs efficiently.