Find Subarray with Zero Sum Using Hash Map

Given an integer array, check if there exists a subarray (of size at least 1) whose sum is 0. Return true if such a subarray exists, else false.

Difficulty:

JavaScript Solution

function subarrayZeroSum(nums) {
  const set = new Set();
  let sum = 0;
  set.add(0);
  for (let num of nums) {
    sum += num;
    if (set.has(sum)) return true;
    set.add(sum);
  }
  return false;
}

Explanation: We maintain prefix sums in a set. If any prefix sum repeats, the subarray between them has sum zero.

⏱ O(n) | 💾 O(n)

Java Solution

class Solution {
  public boolean subarrayZeroSum(int[] nums) {
    Set<Integer> set = new HashSet<>();
    int sum = 0;
    set.add(0);
    for(int num:nums){
      sum += num;
      if(set.contains(sum)) return true;
      set.add(sum);
    }
    return false;
  }
}

Explanation: Use HashSet to store prefix sums. Repeating sums indicate a zero-sum subarray exists.

⏱ O(n) | 💾 O(n)

Python Solution

def subarray_zero_sum(nums):
    s = set()
    total = 0
    s.add(0)
    for num in nums:
        total += num
        if total in s:
            return True
        s.add(total)
    return False

Explanation: Keep cumulative sum in a set. A repeated sum means a subarray sum is zero.

⏱ O(n) | 💾 O(n)

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Find Subarray with Zero Sum Using Hash Map