Subarray Sum(lintcode 138)

Description

Given an integer array, find a subarray where the sum of numbers is zero. Your code should return the index of the first number and the index of the last number.

Notice:
There is at least one subarray that it's sum equals to zero.

Example

Given [-3, 1, 2, -3, 4], return [0, 2] or [1, 3].

Interface

public class Solution {
    /**
     * @param nums: A list of integers
     * @return: A list of integers includes the index of the first number 
     *          and the index of the last number
     */
    public ArrayList<Integer> subarraySum(int[] nums) {
        // write your code here
    }
}

Solution

public class Solution {
    /**
     * @param nums: A list of integers
     * @return: A list of integers includes the index of the first number 
     *          and the index of the last number
     */
    public ArrayList<Integer> subarraySum(int[] nums) {
        // write your code here
        ArrayList<Integer> res = new ArrayList<>();
        HashMap<Integer, Integer> map = new HashMap<>();
        int sum = 0;
        map.put(0, -1);

        for (int i = 0; i < nums.length; ++i) {
            sum += nums[i];
            if (map.containsKey(sum)) {
                res.add(map.get(sum) + 1);
                res.add(i);
                return res;
            }

            map.put(sum, i);
        }

        return res;
    }
}