分治法和归并排序

"""
分治法：
    归并排序：分解原问题为若干个子问题，解决这些子问题，递归求解子问题
    合并子问题的解，成为原问题的解
"""

def merge_sort(seq):
    if len(seq) <= 1:
        return seq
    else:
        mid = int(len(seq)/2)
        left_half = merge_sort(seq[:mid])
        right_half = merge_sort(seq[mid:])
        
    new_seq = merge_sorted_list(left_half, right_half)
    return new_seq
    
def merge_sorted_list(sorted_a, sorted_b):
    length_a, length_b = len(sorted_a), len(sorted_b)
    a = b = 0
    new_sorted_list = []
    
    while a < length_a and b < length_b:
        if sorted_a[a] < sorted_b[b]:
            new_sorted_list.append(sorted_a[a])
            a += 1
        else:
            new_sorted_list.append(sorted_b[b])
            b += 1
    while a < length_a:
        new_sorted_list.append(sorted_a[a])
        a += 1
    while b < length_b:
        new_sorted_list.append(sorted_b[b])
        b += 1
    return new_sorted_list
    
    
def test_merge_sorte():
    import random
    seq = list(range(10))
    random.shuffle(seq)
    assert merge_sort(seq) == sorted(seq)
    assert 0