归并排序--Python

def merg_sort(lst):
    if(len(lst) <= 1):  return lst
    left = merg_sort(lst[:len(lst)/2])
    right = merg_sort(lst[len(lst)/2:len(lst)])
    result = []
    while len(left) > 0 and len(right)> 0:
        if( left[0] > right[0]):
            result.append(right.pop(0))
        else:
            result.append(left.pop(0))
 
    if(len(left)>0): result.extend(merg_sort(left))
    else: result.extend(merg_sort(right))
 
    return result
 
print merg_sort([8,7,43,2,5])

另一种：

#! /usr/bin/env python
# coding: utf-8
 
def merge(arraylist, first, middle, last):
    temp = []
    i = first
    j = middle + 1
    while i <= middle and j <= last:
        if arraylist[i] <= arraylist[j]:
            temp.append(arraylist[i])
            i += 1
        else:
            temp.append(arraylist[j])
            j += 1
    while i <= middle:
        temp.append(arraylist[i])
        i += 1
    while j <= last:
        temp.append(arraylist[j])
        j += 1
    for i in range(0, last - first + 1):
        arraylist[first + i] = temp[i]
 
def merge_sort(arraylist, first, last):
    if first < last:
        middle = (first + last) / 2
        merge_sort(arraylist, first, middle)  
        merge_sort(arraylist, middle + 1, last)
        merge(arraylist, first, middle, last)
 
if __name__ == "__main__":
    arr = [33, 31, 0, 42, 425, 21, 34, 19]
    print arr
    merge_sort(arr, 0, len(arr) - 1)
    print arr