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Special case of k=0
Find the number of subarrays summing to . This is the case of Subarray Sum Equals K. observation: subarray sums to iff . Count pairs of equal prefix sums.
If a prefix sum appears times, it contributes zero-sum subarrays. Try it on . Prefix sums: . Sum appears times: subarrays. Sum appears times: subarray. Total: .
