Find the length of longest continuous subarray within an array (containing at least one number) whose sum equals zero.

For example, given the array [1,0,-1,2],

The longest continuous subarray of zero-sum is [1,0,-1] , which has length = 3.

Python prototype:

```
class Solution(object):
def longestContinousZeroSumSubArray(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
```