Python归并排序（递归实现）

为什么归并排序如此有用？
1. 快捷和稳定
归并排序成为⼀一个非常棒的排序算法主要是因为它的快捷和稳
定。它的复杂度即使在最差情况下都是O(n log n)。而快速排序
在最差情况下的复杂度是O(n^2)，当n=20的时候，它比归并要
慢4.6倍。

2.容易实现

#coding:utf-8
def merge_sort(array):
length = len(array)
if length <= 1: return array
m = length / 2
left = array[:m]
right = array[m:]
left = merge_sort(left)
right = merge_sort(right)
return merge(left,right)

def merge(left,right):
result = []
while len(left)>0 and len(right)>0 :
if left[0] <= right[0]:
result.append(left.pop(0))
else:
result.append(right.pop(0))
result.extend(left)
result.extend(right)
return result

if __name__ == '__main__':
print merge_sort([33,11,2,3,7,2234234234234234,4,23,2,3,4,7])
print merge_sort([0,1,2,3,4,5,5,6,7,8,9])
print merge_sort([9,8,7,6,5,5,4,3,2,1,0])