A C++ function should count the contiguous subarrays whose sum equals a target using a prefix-sum frequency map, but it has several bugs. Find and fix them with minimal changes.

A C++ function should count the contiguous subarrays of an integer array whose sum equals a target (the answer fits in an int). It keeps a hash map from prefix sum to frequency, which starts with the entry 0 mapped to 0. For each element it adds the element to the running sum, increments the map entry for the running sum, and then, if the map contains the running sum minus the target, sets the result to that entry's frequency. Find the bugs and fix them with minimal changes.