自定义比较排序/运算符
1.cmp函数
2.重写类方法
Python3实现各种排序方法
自定义比较排序/运算符Python3和Python2相比有挺多变化。
在Python2中可以直接写一个cmp函数作为参数传入sort来自定义排序，但是Python3取消了。
在这里总结一下Python3的自定义排序的两种写法，欢迎补充。
我们以二维空间中的点来作为待排序的数据结构，我们希望能先比较x后再比较y。
class Pos:
def __init__(self, x = 0, y = 0):
self.x = x
self.y = y
def __str__(self):
return ('(%s, %s)' % (self.x, self.y))
__repr__ = __str__
1.cmp函数
第一种方法我们还是以重写cmp或lambda表达式的形式，和Python2很类似
注意，此方法用sorted是不能成功排序的
只是要借助functools
import functools
def cmp(a, b):
return a.x-b.x if a.x != b.x else a.y-b.y # x y均按照从小到大的顺序
if __name__ == '__main__':
test_list = [Pos(5, 1), Pos(2,5), Pos(2, 4)]
# test_list.sort(key=functools.cmp_to_key(lambda a,b: a.x-b.x if a.x != b.x else a.y-b.y))
test_list.sort(key=functools.cmp_to_key(cmp))
# sorted(test_list, key=functools.cmp_to_key(cmp)) # 亲测此方法不能成功排序
print(test_list) # 输出结果 [(2, 4), (2, 5), (5, 1)]
2.重写类方法
Python2中可以直接重写__cmp__方法来实现比较，但是Python3中已经取消了.
Python3中需要细分每一个比较运算符.
__lt__: <
__gt__: >
__ge__: >=
__eq__: ==
__le__: <=
实现如下
class Pos:
def __init__(self, x = 0, y = 0):
self.x = x
self.y = y
def __str__(self):
return ('(%s, %s)' % (self.x, self.y))
def __lt__(self, other):
print('lt: ' + str(self))
return self.x < other.x if self.x != other.x else self.y < other.y
def __gt__(self, other):
print('gt: ' + str(self))
return self.x > other.x if self.x != other.x else self.y > other.y
def __ge__(self, other):
print('ge: ' + str(self))
return self.x >= other.x if self.x != other.x else self.y >= other.y
def __eq__(self, other):
print('eq: ' + str(self))
return self.x == other.x and self.y == other.y
def __le__(self, other):
print('le: ' + str(self))
return self.x <= other.x if self.x != other.x else self.y <= other.y
__repr__ = __str__
我们实践一下
if __name__ == '__main__':
if Pos(5,1) <= Pos(2,4):
print('True!')
if Pos(5,1) == Pos(2,4):
print('True!')
if Pos(5,1) > Pos(2,4):
print('True!')
# 输出
# le: (5, 1)
# eq: (5, 1)
# gt: (5, 1)
# True!
最后我们回到排序
if __name__ == '__main__':
test_list = [Pos(5, 1), Pos(2,5), Pos(2, 4)]
test_list.sort()
print(test_list)
test_list.sort(reverse=True)
print(test_list)
# 输出
# lt: (2, 5)
# lt: (2, 4)
# [(2, 4), (2, 5), (5, 1)]
# lt: (2, 5)
# lt: (2, 4)
# [(5, 1), (2, 5), (2, 4)]
Python3实现各种排序方法
# coding=gbk
import random
from array import array
def swap(lyst,i,j):
temp = lyst[i]
lyst[i] = lyst[j]
lyst[j] = temp
#选择排序，复杂度O(n^2)
def selectionSort(lyst):
i = 0
while i < len(lyst) - 1:
minIndex = i
j = i + 1
while j < len(lyst):
if lyst[j] < lyst[minIndex]:
minIndex = j
j += 1
if minIndex != i:
swap(lyst,minIndex,i)
i += 1
#冒泡排序，复杂的O(n^2)
def bubbleSort(lyst):
n = len(lyst)
while n > 1:
i = 1
while i < n:
if lyst[i] < lyst[i-1]:
swap(lyst,i,i-1)
i += 1
n -= 1
#冒泡排序优化改进最好情况
def bubbleSortWithTweak(lyst):
n = len(lyst)
while n > 1:
swapped = False
i = 1
while i < n:
if lyst[i] < lyst[i-1]:
swap(lyst,i,i-1)
swapped = True
i += 1
if not swapped: return
n -= 1
#插入排序，复杂的O(n^2)
def insertionSort(lyst):
i = 1
while i < len(lyst):
itemToInsert = lyst[i]
j = i - 1
while j >= 0:
if itemToInsert < lyst[j]:
lyst[j+1] = lyst[j]
j -= 1
else:
break
lyst[j+1] = itemToInsert
i += 1
#快速排序,最好情况，复杂的O(n*(log2 n))，最坏情况，复杂的O(n^2)
def quicksort(lyst):
quicksortHelper(lyst,0,len(lyst)-1)
def quicksortHelper(lyst,left,right):
if left < right:
pivotLocation = partition(lyst,left,right)
quicksortHelper(lyst,left,pivotLocation-1)
quicksortHelper(lyst,pivotLocation+1,right)
def partition(lyst,left,right):
middle = (left+right) // 2
pivot = lyst[middle]
lyst[middle] = lyst[right]
lyst[right] = pivot
boundary = left
for index in range(left,right):
if lyst[index] < pivot:
swap(lyst,index,boundary)
boundary += 1
swap(lyst,right,boundary)
return boundary
#合并排序
def mergeSort(lyst):
copyBuffer = [0]*(len(lyst))
mergeSortHelper(lyst,copyBuffer,0,len(lyst)-1)
def mergeSortHelper(lyst,copyBuffer,low,high):
if low < high:
middle = (low+high)//2
mergeSortHelper(lyst,copyBuffer,low,middle)
mergeSortHelper(lyst,copyBuffer,middle+1,high)
merge(lyst,copyBuffer,low,middle,high)
def merge(lyst,copyBuffer,low,middle,high):
i1 = low
i2 = middle + 1
for i in range(low,high+1):
if i1 > middle:
copyBuffer[i] = lyst[i2]
i2 += 1
elif i2 > high:
copyBuffer[i] = lyst[i1]
i1 += 1
elif lyst[i1] < lyst[i2]:
copyBuffer[i] = lyst[i1]
i1 += 1
else :
copyBuffer[i] = lyst[i2]
i2 += 1
for i in range(low,high+1):
lyst[i] = copyBuffer[i]
def main(size = 20,sort = mergeSort):
lyst = []
for count in range(size):
lyst.append(random.randint(1,size+1))
print(lyst)
sort(lyst)
print(lyst)
if __name__ == "__main__":
main()
以上为个人经验，希望能给大家一个参考，也希望大家多多支持易知道(ezd.cc)。
