jPycV7 - Online Java Compiler & Debugging Tool

/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		int[] arr =  {15, -2, 2, -8, 1, 7, 10};
		System.out.println("longest subarray with sum zero is " + longestSubarrayWithSumZero(arr));
	}
	static int longestSubarrayWithSumZero(int[] arr){
		HashMap<Integer,Integer> map = new HashMap<>();
		map.put(0,-1);
		int prefixSum = 0;
		int max = 0;
		for(int i=0;i<arr.length;i++){
			 prefixSum +=arr[i];
			 if(map.containsKey(prefixSum)){
			 	int leftIndex = map.get(prefixSum);
			 	max = Math.max(max, i-leftIndex);
			 } else
			 map.put(prefixSum,i);
		}
		return max;

	}
}