grokking 234

class Solution {
    public int minSumOfLengths(int[] nums, int target) {
        Map<Integer, Integer> sums = new HashMap<>(); // prefix sum, index
        sums.put(0, -1);

        int sum = 0; // prefix sum
        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            sums.put(sum, i);

            // store prefix sums to nums for the second loop
            nums[i] = sum;
        }

        int ans = Integer.MAX_VALUE;
        int len1 = Integer.MAX_VALUE;
        for (int i = 0; i < nums.length; i++) {
            // Find minimum length of subarray ends at index <= i
            if (sums.containsKey(nums[i] - target)) {
                len1 = Math.min(len1, i - sums.get(nums[i] - target));
            }
            // Find length of subarray starts at index <= i
            if (sums.containsKey(nums[i] + target) && len1 < Integer.MAX_VALUE) {
                int len2 = sums.get(nums[i] + target) - i;
                ans = Math.min(ans, len1 + len2);
            }
        }

        return ans == Integer.MAX_VALUE ? -1 : ans;
    }
}