325. Maximum Size Subarray Sum Equals k

Given an array nums and a target value k , find the maximum length of a subarray that sums to k . If there isn't one, return 0 instead.

Note:
The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range.

Example 1:

Input: 

nums

 = 
[1, -1, 5, -2, 3]

, 
k

 = 
3

Output: 

4 
Explanation: 

The subarray 
[1, -1, 5, -2]

 sums to 3 and is the longest.

Example 2:

Input: 

nums

 = 
[-2, -1, 2, 1]

, 
k

 = 
1

Output: 

2 

Explanation: 

The subarray 
[-1, 2]

 sums to 1 and is the longest.

Follow Up:
Can you do it in O( n ) time