Poison

930. Binary Subarrays With Sum

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class Solution {
    public int numSubarraysWithSum(int[] nums, int goal) {
        int preSum = 0, count = 0;
        Map<Integer, Integer> preSumToCountMap = new HashMap<>();
        preSumToCountMap.put(0, 1);
        for (int num : nums) {
            preSum += num;
            count += preSumToCountMap.getOrDefault(preSum - goal, 0);
            preSumToCountMap.put(preSum, preSumToCountMap.getOrDefault(preSum, 0) + 1);
        }

        return count;
    }
}
Reference

930. Binary Subarrays With Sum