In the max subarray problem, if we always overwrite the prefix_map entry for a given prefix_sum with the current index instead of only setting it once, how does that affect the calculation of the longest subarray length?

In the classic max subarray problem using prefix sums, we maintain a map from each prefix sum value to the earliest index where it occurs. This allows us to compute the length of a zero‑sum subarray ending at the current index as i - earliest_index. If we overwrite the map entry with the current index every time we see the same prefix sum, we lose the earliest occurrence. Consequently, any subarray that would have used that earlier index to achieve a longer span will no longer be considered. The algorithm will still find a maximum subarray, but its length may be smaller than the true maximum because the map no longer holds the optimal starting point. In the worst case, if a prefix sum repeats many times, the longest subarray could be missed entirely. The time complexity remains O(n) and space O(n), but the correctness of the longest length is compromised.