Algorithm

Initialize a variable sum = 0, which stores the sum of elements traversed so far, and another variable max = 0, which stores the length of the longest subarray with sum zero.
Declare a HashMap<Integer, Integer> to store the prefix sum of every element as a key and its index as a value.
Traverse the array and add the array element to the sum.
If sum = 0, update max with the maximum value between max and current_index + 1, as the subarray from the start to the current index has a sum of 0.
If sum is not equal to zero, check the HashMap to see if we've encountered this sum before.
If the HashMap contains the sum, this indicates that a subarray with the same sum exists, so update max accordingly.
If the sum is not found in the HashMap, insert (sum, current_index) into the HashMap to store the prefix sum until the current index.
After traversing the entire array, the max variable will hold the length of the longest subarray with a sum equal to zero. Return max.

Code

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