Merge Sort

# Merge Sort

Zerethon Official Sample `merge-sort`, version 1.0.0, Python 3.12.

- `merge_sort.py` — the algorithm, as shown in Zerethon Tools
- `main.py` — entry file: a short demonstration
- `test_merge_sort.py` — checks; set it as the entry file to run them

This project is your own copy. Changing it never changes the official sample.
See the algorithm animated: https://tools.zerethon.com/merge-sort-visualizer

from merge_sort import merge_sort

numbers = [38, 27, 43, 3, 9, 82, 10, 27]
print("Before:", numbers)
result = merge_sort(list(numbers))
print("After: ", result)
print("Same as sorted():", result == sorted(numbers))

"""Merge Sort (Zerethon Official Sample: merge-sort 1.0.0)."""


def merge_sort(a):
    if len(a) <= 1:
        return a
    mid = len(a) // 2
    left = merge_sort(a[:mid])
    right = merge_sort(a[mid:])
    out, i, j = [], 0, 0
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            out.append(left[i]); i += 1
        else:
            out.append(right[j]); j += 1
    out.extend(left[i:])
    out.extend(right[j:])
    return out

# Checks for merge_sort. To run them, set this file as the entry file
# (the ▶ button next to it in Files) and press Run.
from merge_sort import merge_sort


def numbers(seed, count):
    """Deterministic pseudo-random integers in [-50, 49]."""
    out = []
    for _ in range(count):
        seed = (seed * 1103515245 + 12345) % 2**31
        out.append(seed % 100 - 50)
    return out


cases = [[], [1], [2, 1], [1, 2, 3], [3, 2, 1], [5, 1, 5, 1, 5], [-3, 0, -1, 2]]
cases += [numbers(seed, size) for seed, size in ((1, 10), (2, 50), (3, 200))]

for case in cases:
    got = merge_sort(list(case))
    assert got == sorted(case), f"merge_sort({case[:6]}...) = {got[:6]}..."

print(f"All {len(cases)} checks passed.")