Find Two Non-overlapping Sub-arrays Each With Target Sum

Given an array of integers arr and an integer target.

You have to find two non-overlapping sub-arrays of arr each with sum equal target. There can be multiple answers so you have to find an answer where the sum of the lengths of the two sub-arrays is minimum.

Return the minimum sum of the lengths of the two required sub-arrays, or return -1 if you cannot find such two sub-arrays.

Example 1:

Input: arr = [3,2,2,4,3], target = 3
Output: 2
Explanation: Only two sub-arrays have sum = 3 ([3] and [3]). The sum of their lengths is 2.

Example 2:

Input: arr = [7,3,4,7], target = 7
Output: 2
Explanation: Although we have three non-overlapping sub-arrays of sum = 7 ([7], [3,4] and [7]), but we will choose the first and third sub-arrays as the sum of their lengths is 2.

Example 3:

Input: arr = [4,3,2,6,2,3,4], target = 6
Output: -1
Explanation: We have only one sub-array of sum = 6.

Example 4:

Input: arr = [5,5,4,4,5], target = 3
Output: -1
Explanation: We cannot find a sub-array of sum = 3.

Example 5:

Input: arr = [3,1,1,1,5,1,2,1], target = 3
Output: 3
Explanation: Note that sub-arrays [1,2] and [2,1] cannot be an answer because they overlap.

Constraints:

• 1 <= arr.length <= 10^5

• 1 <= arr[i] <= 1000

• 1 <= target <= 10^8

class Solution {
    public int minSumOfLengths(int[] arr, int target) {
        // Map of prefix sum -> index
        HashMap<Integer, Integer> hmap = new HashMap<>();
        int sum = 0;
        hmap.put(0, -1);
        for (int i = 0; i < arr.length; i++) {
            sum += arr[i];
            hmap.put(sum, i);
        }
        sum = 0;
        int lsize = Integer.MAX_VALUE, result = Integer.MAX_VALUE;
        for (int i = 0; i < arr.length; i++) {
            sum += arr[i];
            if (hmap.get(sum - target) != null) {
                // stores minimum length of sub-array ending with index<= i with sum target.
                // This ensures non- overlapping property.
                lsize = Math.min(lsize, i - hmap.get(sum - target));
            }
            // hmap.get(sum+target) searches for any sub-array starting with index i+1 with
            // sum target.
            if (hmap.get(sum + target) != null && lsize < Integer.MAX_VALUE) {
                // updates the result only if both left and right sub-array
                // exists.
                result = Math.min(result, hmap.get(sum + target) - i + lsize);
            }
        }
        return result == Integer.MAX_VALUE ? -1 : result;
    }
}