Unexpected Output When Implementing Merge Sort with Inversion Counting in Python
I tried several approaches but none seem to work. I'm stuck trying to I'm sure I'm missing something obvious here, but After trying multiple solutions online, I still can't figure this out... I'm currently working on implementing the Merge Sort algorithm in Python, and I want to count the number of inversions in the array simultaneously. However, I’m working with unexpected outputs when testing with larger datasets. The implementation seems correct at a glance, but it fails to count some inversions accurately. Here's a simplified version of my code: ```python def merge_and_count(arr, temp_arr, left, mid, right): i = left # Starting index for left subarray j = mid + 1 # Starting index for right subarray k = left # Starting index to be sorted inv_count = 0 while i <= mid and j <= right: if arr[i] <= arr[j]: temp_arr[k] = arr[i] i += 1 else: temp_arr[k] = arr[j] inv_count += (mid - i + 1) j += 1 k += 1 while i <= mid: temp_arr[k] = arr[i] i += 1 k += 1 while j <= right: temp_arr[k] = arr[j] j += 1 k += 1 for i in range(left, right + 1): arr[i] = temp_arr[i] return inv_count def merge_sort_and_count(arr, temp_arr, left, right): inv_count = 0 if left < right: mid = (left + right) // 2 inv_count += merge_sort_and_count(arr, temp_arr, left, mid) inv_count += merge_sort_and_count(arr, temp_arr, mid + 1, right) inv_count += merge_and_count(arr, temp_arr, left, mid, right) return inv_count arr = [1, 20, 6, 4, 5] temp_arr = [0] * len(arr) result = merge_sort_and_count(arr, temp_arr, 0, len(arr) - 1) print(f'Number of inversions: {result}') # Expected output: 5 ``` I've tested it with the input `[1, 20, 6, 4, 5]`, which should return `5` inversions. However, when I test with larger arrays like `[8, 4, 2, 1, 3, 6, 5]`, I receive incorrect results, and in some cases, it returns `0` inversions. I suspect that the indices being used might be going out of bounds or that the inversion count isn’t being aggregated correctly. I’ve also printed intermediate results to debug, but everything looks fine during those checks. Does anyone have insights on what might be going wrong or how I can debug this further? Any suggestions for edge cases I should consider? Thanks! Is there a better approach? Am I approaching this the right way? I recently upgraded to Python latest. Any ideas how to fix this? I'm using Python 3.10 in this project. Am I missing something obvious?