python中归并排序

 1 # coding=UTF-8
 2 #!/usr/bin/python
 3 
 4 import sys
 5 
 6 def merge(nums, first, middle, last):
 7     "merge"
 8     #切片边界，左闭右开，从0开始
 9     lnums = nums[ first:middle+1 ]
10     rnums = nums[ middle+1:last+1 ]
11     lnums.append(sys.maxint)
12     rnums.append(sys.maxint)
13     l = 0
14     r = 0
15     for i in range( first, last+1 ):
16         if lnums[l] < rnums[r]:
17             nums[i] = lnums[l]
18             l+=1
19         else:
20             nums[i] = rnums[r]
21             r+=1
22 
23 def merge_sort(nums, first, last):
24     """mergesort
25         mergesort函数中传递的是下标，不是元素的个数
26     """28     if first < last:
29         middle = (first + last)/2
30         #print "middle in loop", count, "is:", middle
32         merge_sort(nums, first, middle)
33         merge_sort(nums, middle+1, last)
34         merge(nums,first, middle, last)
35         #print "loops:",count,">>", nums
36 
37 
38 
39 if __name__ == ‘__main__‘:
40     nums = [10, 8, 4, -1, 2, 6, 7, 3]
41     print "nums is ", nums
42     merge_sort(nums, 0, 7)
43     print "merge_sort", nums