用Python合并排序
我找不到任何可用的Python3.3合并排序算法代码,所以我自己做了一个。有没有办法加快速度?它在大约0.3-0.5秒内对20000个数字进行排序用Python合并排序,python,python-3.x,algorithm,sorting,mergesort,Python,Python 3.x,Algorithm,Sorting,Mergesort,我找不到任何可用的Python3.3合并排序算法代码,所以我自己做了一个。有没有办法加快速度?它在大约0.3-0.5秒内对20000个数字进行排序 def msort(x): result = [] if len(x) < 2: return x mid = int(len(x)/2) y = msort(x[:mid]) z = msort(x[mid:]) while (len(y) > 0) or (len(z)
def msort(x):
result = []
if len(x) < 2:
return x
mid = int(len(x)/2)
y = msort(x[:mid])
z = msort(x[mid:])
while (len(y) > 0) or (len(z) > 0):
if len(y) > 0 and len(z) > 0:
if y[0] > z[0]:
result.append(z[0])
z.pop(0)
else:
result.append(y[0])
y.pop(0)
elif len(z) > 0:
for i in z:
result.append(i)
z.pop(0)
else:
for i in y:
result.append(i)
y.pop(0)
return result
def msort(x):
结果=[]
如果len(x)<2:
返回x
mid=int(len(x)/2)
y=msort(x[:mid])
z=msort(x[mid:]
而(len(y)>0)或(len(z)>0):
如果len(y)>0且len(z)>0:
如果y[0]>z[0]:
result.append(z[0])
z、 流行音乐(0)
其他:
结果.追加(y[0])
y、 流行音乐(0)
elif len(z)>0:
对于z中的i:
结果.追加(i)
z、 流行音乐(0)
其他:
对于y中的i:
结果.追加(i)
y、 流行音乐(0)
返回结果
这样的循环可能会加速:
for i in z:
result.append(i)
z.pop(0)
相反,只需这样做:
result.extend(z)
请注意,无需清理
z
的内容,因为您无论如何都不会使用它。您可以在mergesort的顶级调用中初始化整个结果列表:
result = [0]*len(x) # replace 0 with a suitable default element if necessary.
# or just copy x (result = x[:])
然后,对于递归调用,您可以使用一个helper函数,向该函数传递的不是子列表,而是索引到x
。底层调用从x
读取它们的值,并直接写入result
通过这种方式,您可以避免所有应该提高性能的
pop
ing和append
ing。第一个改进是简化主循环中的三种情况:与其在某些序列有元素时迭代,不如在两个序列都有元素时迭代。离开循环时,其中一个将为空,我们不知道是哪个,但我们不在乎:我们将它们附加到结果的末尾
def msort2(x):
if len(x) < 2:
return x
result = [] # moved!
mid = int(len(x) / 2)
y = msort2(x[:mid])
z = msort2(x[mid:])
while (len(y) > 0) and (len(z) > 0):
if y[0] > z[0]:
result.append(z[0])
z.pop(0)
else:
result.append(y[0])
y.pop(0)
result += y
result += z
return result
最后一个改进是使用非递归算法对短序列进行排序。在这种情况下,我使用内置的sorted
功能,并在输入大小小于20时使用它:
def msort4(x):
if len(x) < 20:
return sorted(x)
result = []
mid = int(len(x) / 2)
y = msort4(x[:mid])
z = msort4(x[mid:])
i = 0
j = 0
while i < len(y) and j < len(z):
if y[i] > z[j]:
result.append(z[j])
j += 1
else:
result.append(y[i])
i += 1
result += y[i:]
result += z[j:]
return result
def msort4(x):
如果len(x)<20:
返回排序(x)
结果=[]
mid=int(len(x)/2)
y=msort4(x[:中间])
z=msort4(x[mid:]
i=0
j=0
而iz[j]:
result.append(z[j])
j+=1
其他:
结果.追加(y[i])
i+=1
结果+=y[i:]
结果+=z[j:]
返回结果
我对100000个整数的随机列表进行排序的测量结果是,原始版本为2.46秒,msort2为2.33秒,msort3为0.60秒,msort4为0.40秒。作为参考,使用
排序的对所有列表进行排序需要0.03秒。一个较长的列表,用于计算倒数并遵循排序的界面。修改它,使其成为一个适当排序的对象的方法,这很简单
import operator
class MergeSorted:
def __init__(self):
self.inversions = 0
def __call__(self, l, key=None, reverse=False):
self.inversions = 0
if key is None:
self.key = lambda x: x
else:
self.key = key
if reverse:
self.compare = operator.gt
else:
self.compare = operator.lt
dest = list(l)
working = [0] * len(l)
self.inversions = self._merge_sort(dest, working, 0, len(dest))
return dest
def _merge_sort(self, dest, working, low, high):
if low < high - 1:
mid = (low + high) // 2
x = self._merge_sort(dest, working, low, mid)
y = self._merge_sort(dest, working, mid, high)
z = self._merge(dest, working, low, mid, high)
return (x + y + z)
else:
return 0
def _merge(self, dest, working, low, mid, high):
i = 0
j = 0
inversions = 0
while (low + i < mid) and (mid + j < high):
if self.compare(self.key(dest[low + i]), self.key(dest[mid + j])):
working[low + i + j] = dest[low + i]
i += 1
else:
working[low + i + j] = dest[mid + j]
inversions += (mid - (low + i))
j += 1
while low + i < mid:
working[low + i + j] = dest[low + i]
i += 1
while mid + j < high:
working[low + i + j] = dest[mid + j]
j += 1
for k in range(low, high):
dest[k] = working[k]
return inversions
msorted = MergeSorted()
这是另一个解决方案
class MergeSort(object):
def _merge(self,left, right):
nl = len(left)
nr = len(right)
result = [0]*(nl+nr)
i=0
j=0
for k in range(len(result)):
if nl>i and nr>j:
if left[i] <= right[j]:
result[k]=left[i]
i+=1
else:
result[k]=right[j]
j+=1
elif nl==i:
result[k] = right[j]
j+=1
else: #nr>j:
result[k] = left[i]
i+=1
return result
def sort(self,arr):
n = len(arr)
if n<=1:
return arr
left = self.sort(arr[:n/2])
right = self.sort(arr[n/2:] )
return self._merge(left, right)
def main():
import random
a= range(100000)
random.shuffle(a)
mr_clss = MergeSort()
result = mr_clss.sort(a)
#print result
if __name__ == '__main__':
main()
def合并(l1、l2、out=[]):
如果l1=[]:返回+l2
如果l2=[]:返回+l1
如果l1[0]def merge_sort(x):
如果len(x)<2:返回x
结果,mid=[],int(len(x)/2)
y=合并\排序(x[:中间])
z=合并\排序(x[mid:])
而(len(y)>0)和(len(z)>0):
如果y[0]>z[0]:result.append(z.pop(0))
else:result.append(y.pop(0))
结果.扩展(y+z)
返回结果
接受我的实现
def merge_sort(sequence):
"""
Sequence of numbers is taken as input, and is split into two halves, following which they are recursively sorted.
"""
if len(sequence) < 2:
return sequence
mid = len(sequence) // 2 # note: 7//2 = 3, whereas 7/2 = 3.5
left_sequence = merge_sort(sequence[:mid])
right_sequence = merge_sort(sequence[mid:])
return merge(left_sequence, right_sequence)
def merge(left, right):
"""
Traverse both sorted sub-arrays (left and right), and populate the result array
"""
result = []
i = j = 0
while i < len(left) and j < len(right):
if left[i] < right[j]:
result.append(left[i])
i += 1
else:
result.append(right[j])
j += 1
result += left[i:]
result += right[j:]
return result
# Print the sorted list.
print(merge_sort([5, 2, 6, 8, 5, 8, 1]))
def merge_排序(顺序):
"""
数字序列作为输入,被分成两半,然后递归排序。
"""
如果len(序列)<2:
返回序列
mid=len(序列)//2#注:7//2=3,而7/2=3.5
左\序列=合并\排序(序列[:中间])
右\序列=合并\排序(序列[mid:])
返回合并(左\u序列、右\u序列)
def合并(左、右):
"""
遍历已排序的两个子数组(左侧和右侧),并填充结果数组
"""
结果=[]
i=j=0
而i
试试这个递归版本
def mergeList(l1,l2):
l3=[]
Tlen=len(l1)+len(l2)
inf= float("inf")
for i in range(Tlen):
print "l1= ",l1[0]," l2= ",l2[0]
if l1[0]<=l2[0]:
l3.append(l1[0])
del l1[0]
l1.append(inf)
else:
l3.append(l2[0])
del l2[0]
l2.append(inf)
return l3
def main():
l1=[2,10,7,6,8]
print mergeSort(breaklist(l1))
def breaklist(rawlist):
newlist=[]
for atom in rawlist:
print atom
list_atom=[atom]
newlist.append(list_atom)
return newlist
def mergeSort(inputList):
listlen=len(inputList)
if listlen ==1:
return inputList
else:
newlist=[]
if listlen % 2==0:
for i in range(listlen/2):
newlist.append(mergeList(inputList[2*i],inputList[2*i+1]))
else:
for i in range((listlen+1)/2):
if 2*i+1<listlen:
newlist.append(mergeList(inputList[2*i],inputList[2*i+1]))
else:
newlist.append(inputList[2*i])
return mergeSort(newlist)
if __name__ == '__main__':
main()
def合并列表(l1、l2):
l3=[]
Tlen=len(l1)+len(l2)
inf=浮动(“inf”)
对于范围内的i(Tlen):
打印“l1=”,l1[0],“l2=”,l2[0]
如果l1[0]如前所述,l.pop(0)
是一个O(len(l))操作并且必须避免,则上述msort函数是O(n**2)。如果效率重要的话,索引更好,但也有成本。l中x的更快,但对于mergesort不容易实现:iter
可以在这里使用。最后,检查i
两次,因为在访问元素时再次测试:异常机制(try-except)更好,最后改进了30%
def msort(l):
if len(l)>1:
t=len(l)//2
it1=iter(msort(l[:t]));x1=next(it1)
it2=iter(msort(l[t:]));x2=next(it2)
l=[]
try:
while True:
if x1<=x2: l.append(x1);x1=next(it1)
else : l.append(x2);x2=next(it2)
except:
if x1<=x2: l.append(x2);l.extend(it2)
else: l.append(x1);l.extend(it1)
return l
def msort(l):
如果len(l)>1:
t=len(l)//2
it1=国际热核实验堆(msort(l[:t]);x1=下一个(it1)
it2=国际热核实验堆(msort(l[t:]);x2=下一个(it2)
l=[]
尝试:
尽管如此:
如果x1代码来自麻省理工学院课程。(与通用合作伙伴一起)
import operator
def merge(left, right, compare):
result = []
i, j = 0, 0
while i < len(left) and j < len(right):
if compare(left[i], right[j]):
result.append(left[i])
i += 1
else:
result.append(right[j])
j += 1
while i < len(left):
result.append(left[i])
i += 1
while j < len(right):
result.append(right[j])
j += 1
return result
def mergeSort(L, compare=operator.lt):
if len(L) < 2:
return L[:]
else:
middle = int(len(L) / 2)
left = mergeSort(L[:middle], compare)
right = mergeSort(L[middle:], compare)
return merge(left, right, compare)
导入操作符
def合并(左、右、比较):
结果=[]
i、 j=0,0
而i
晚会有点晚了,但我想我会放弃我的梦想
def merge_sort(x):
if len(x) < 2:return x
result,mid = [],int(len(x)/2)
y = merge_sort(x[:mid])
z = merge_sort(x[mid:])
while (len(y) > 0) and (len(z) > 0):
if y[0] > z[0]:result.append(z.pop(0))
else:result.append(y.pop(0))
result.extend(y+z)
return result
def merge_sort(sequence):
"""
Sequence of numbers is taken as input, and is split into two halves, following which they are recursively sorted.
"""
if len(sequence) < 2:
return sequence
mid = len(sequence) // 2 # note: 7//2 = 3, whereas 7/2 = 3.5
left_sequence = merge_sort(sequence[:mid])
right_sequence = merge_sort(sequence[mid:])
return merge(left_sequence, right_sequence)
def merge(left, right):
"""
Traverse both sorted sub-arrays (left and right), and populate the result array
"""
result = []
i = j = 0
while i < len(left) and j < len(right):
if left[i] < right[j]:
result.append(left[i])
i += 1
else:
result.append(right[j])
j += 1
result += left[i:]
result += right[j:]
return result
# Print the sorted list.
print(merge_sort([5, 2, 6, 8, 5, 8, 1]))
def mergeList(l1,l2):
l3=[]
Tlen=len(l1)+len(l2)
inf= float("inf")
for i in range(Tlen):
print "l1= ",l1[0]," l2= ",l2[0]
if l1[0]<=l2[0]:
l3.append(l1[0])
del l1[0]
l1.append(inf)
else:
l3.append(l2[0])
del l2[0]
l2.append(inf)
return l3
def main():
l1=[2,10,7,6,8]
print mergeSort(breaklist(l1))
def breaklist(rawlist):
newlist=[]
for atom in rawlist:
print atom
list_atom=[atom]
newlist.append(list_atom)
return newlist
def mergeSort(inputList):
listlen=len(inputList)
if listlen ==1:
return inputList
else:
newlist=[]
if listlen % 2==0:
for i in range(listlen/2):
newlist.append(mergeList(inputList[2*i],inputList[2*i+1]))
else:
for i in range((listlen+1)/2):
if 2*i+1<listlen:
newlist.append(mergeList(inputList[2*i],inputList[2*i+1]))
else:
newlist.append(inputList[2*i])
return mergeSort(newlist)
if __name__ == '__main__':
main()
def msort(l):
if len(l)>1:
t=len(l)//2
it1=iter(msort(l[:t]));x1=next(it1)
it2=iter(msort(l[t:]));x2=next(it2)
l=[]
try:
while True:
if x1<=x2: l.append(x1);x1=next(it1)
else : l.append(x2);x2=next(it2)
except:
if x1<=x2: l.append(x2);l.extend(it2)
else: l.append(x1);l.extend(it1)
return l
import operator
def merge(left, right, compare):
result = []
i, j = 0, 0
while i < len(left) and j < len(right):
if compare(left[i], right[j]):
result.append(left[i])
i += 1
else:
result.append(right[j])
j += 1
while i < len(left):
result.append(left[i])
i += 1
while j < len(right):
result.append(right[j])
j += 1
return result
def mergeSort(L, compare=operator.lt):
if len(L) < 2:
return L[:]
else:
middle = int(len(L) / 2)
left = mergeSort(L[:middle], compare)
right = mergeSort(L[middle:], compare)
return merge(left, right, compare)
# [Python 3]
def merge_sort(arr):
if len(arr) < 2:
return arr
half = len(arr) // 2
left = merge_sort(arr[:half])
right = merge_sort(arr[half:])
out = []
li = ri = 0 # index of next element from left, right halves
while True:
if li >= len(left): # left half is exhausted
out.extend(right[ri:])
break
if ri >= len(right): # right half is exhausted
out.extend(left[li:])
break
if left[li] < right[ri]:
out.append(left[li])
li += 1
else:
out.append(right[ri])
ri += 1
return out
merge sort: 1.03605 seconds
Python sort: 0.045 seconds
Ratio merge / Python sort: 23.0229
def merge(arr, p, q, r):
n1 = q - p + 1
n2 = r - q
right, left = [], []
for i in range(n1):
left.append(arr[p + i])
for j in range(n2):
right.append(arr[q + j + 1])
left.append(float('inf'))
right.append(float('inf'))
i = j = 0
for k in range(p, r + 1):
if left[i] <= right[j]:
arr[k] = left[i]
i += 1
else:
arr[k] = right[j]
j += 1
def merge_sort(arr, p, r):
if p < r:
q = (p + r) // 2
merge_sort(arr, p, q)
merge_sort(arr, q + 1, r)
merge(arr, p, q, r)
if __name__ == '__main__':
test = [5, 2, 4, 7, 1, 3, 2, 6]
merge_sort(test, 0, len(test) - 1)
print test
[1, 2, 2, 3, 4, 5, 6, 7]
def merge(x):
if len(x) == 1:
return x
else:
mid = int(len(x) / 2)
l = merge(x[:mid])
r = merge(x[mid:])
i = j = 0
result = []
while i < len(l) and j < len(r):
if l[i] < r[j]:
result.append(l[i])
i += 1
else:
result.append(r[j])
j += 1
result += l[i:]
result += r[j:]
return result
def mergeSort(alist):
print("Splitting ",alist)
if len(alist)>1:
mid = len(alist)//2
lefthalf = alist[:mid]
righthalf = alist[mid:]
mergeSort(lefthalf)
mergeSort(righthalf)
i=0
j=0
k=0
while i < len(lefthalf) and j < len(righthalf):
if lefthalf[i] < righthalf[j]:
alist[k]=lefthalf[i]
i=i+1
else:
alist[k]=righthalf[j]
j=j+1
k=k+1
while i < len(lefthalf):
alist[k]=lefthalf[i]
i=i+1
k=k+1
while j < len(righthalf):
alist[k]=righthalf[j]
j=j+1
k=k+1
print("Merging ",alist)
alist = [54,26,93,17,77,31,44,55,20]
mergeSort(alist)
print(alist)
def merge(a,low,mid,high):
l=a[low:mid+1]
r=a[mid+1:high+1]
#print(l,r)
k=0;i=0;j=0;
c=[0 for i in range(low,high+1)]
while(i<len(l) and j<len(r)):
if(l[i]<=r[j]):
c[k]=(l[i])
k+=1
i+=1
else:
c[k]=(r[j])
j+=1
k+=1
while(i<len(l)):
c[k]=(l[i])
k+=1
i+=1
while(j<len(r)):
c[k]=(r[j])
k+=1
j+=1
#print(c)
a[low:high+1]=c
def mergesort(a,low,high):
if(high>low):
mid=(low+high)//2
mergesort(a,low,mid)
mergesort(a,mid+1,high)
merge(a,low,mid,high)
a=[12,8,3,2,9,0]
mergesort(a,0,len(a)-1)
print(a)
def merge_sort(arr):
if len(arr) < 2:
return arr[:]
middle_of_arr = len(arr) / 2
left = arr[0:middle_of_arr]
right = arr[middle_of_arr:]
left_side = merge_sort(left)
right_side = merge_sort(right)
return merge(left_side, right_side)
def merge(left_side, right_side):
result = []
while len(left_side) > 0 or len(right_side) > 0:
if len(left_side) > 0 and len(right_side) > 0:
if left_side[0] <= right_side[0]:
result.append(left_side.pop(0))
else:
result.append(right_side.pop(0))
elif len(left_side) > 0:
result.append(left_side.pop(0))
elif len(right_side) > 0:
result.append(right_side.pop(0))
return result
arr = [6, 5, 4, 3, 2, 1]
# print merge_sort(arr)
# [1, 2, 3, 4, 5, 6]
def mergesort(lis):
if len(lis) > 1:
left, right = map(lambda l: list(reversed(mergesort(l))), (lis[::2], lis[1::2]))
lis.clear()
while left and right:
lis.append(left.pop() if left[-1] < right[-1] else right.pop())
lis.extend(left[::-1])
lis.extend(right[::-1])
return lis
def merge(left,right):
result=[]
i,j=0,0
while i<len(left) and j<len(right):
if left[i] < right[j]:
result.append(left[i])
i+=1
else:
result.append(right[j])
j+=1
result.extend(left[i:]) # since we want to add each element and not the object list
result.extend(right[j:])
return result
def merge_sort(data):
if len(data)==1:
return data
middle=len(data)//2
left_data=merge_sort(data[:middle])
right_data=merge_sort(data[middle:])
return merge(left_data,right_data)
data=[100,5,200,3,100,4,8,9]
print(merge_sort(data))
def merge_sort(array):
n = len(array)
if n > 1:
mid = n//2
left = array[0:mid]
right = array[mid:n]
print(mid, left, right, array)
merge_sort(left)
merge_sort(right)
merge(left, right, array)
def merge(left, right, array):
array_length = len(array)
right_length = len(right)
left_length = len(left)
left_index = right_index = 0
for array_index in range(0, array_length):
if right_index == right_length:
array[array_index:array_length] = left[left_index:left_length]
break
elif left_index == left_length:
array[array_index:array_length] = right[right_index:right_length]
break
elif left[left_index] <= right[right_index]:
array[array_index] = left[left_index]
left_index += 1
else:
array[array_index] = right[right_index]
right_index += 1
array = [99,2,3,3,12,4,5]
arr_len = len(array)
merge_sort(array)
print(array)
assert len(array) == arr_len
import math
def merge_array(ar1, ar2):
c, i, j= [], 0, 0
while i < len(ar1) and j < len(ar2):
if ar1[i] < ar2[j]:
c.append(ar1[i])
i+=1
else:
c.append(ar2[j])
j+=1
return c + ar1[i:] + ar2[j:]
def mergesort(array):
n = len(array)
if n == 1:
return array
half_n = math.floor(n/2)
ar1, ar2 = mergesort(array[:half_n]), mergesort(array[half_n:])
return merge_array(ar1, ar2)
#here is my answer using two function one for merge and another for divide and
#conquer
l=int(input('enter range len'))
c=list(range(l,0,-1))
print('list before sorting is',c)
def mergesort1(c,l,r):
i,j,k=0,0,0
while (i<len(l))&(j<len(r)):
if l[i]<r[j]:
c[k]=l[i]
i +=1
else:
c[k]=r[j]
j +=1
k +=1
while i<len(l):
c[k]=l[i]
i+=1
k+=1
while j<len(r):
c[k]=r[j]
j+=1
k+=1
return c
def mergesort(c):
if len(c)<2:
return c
else:
l=c[0:(len(c)//2)]
r=c[len(c)//2:len(c)]
mergesort(l)
mergesort(r)
return mergesort1(c,l,r)
[1, 2, 3, 4, 5]
from run_time import run_time
from random_arr import make_arr
def merge(arr1: list, arr2: list):
temp = []
x, y = 0, 0
while len(arr1) and len(arr2):
if arr1[0] < arr2[0]:
temp.append(arr1[0])
x += 1
arr1 = arr1[x:]
elif arr1[0] > arr2[0]:
temp.append(arr2[0])
y += 1
arr2 = arr2[y:]
else:
temp.append(arr1[0])
temp.append(arr2[0])
x += 1
y += 1
arr1 = arr1[x:]
arr2 = arr2[y:]
if len(arr1) > 0:
temp += arr1
if len(arr2) > 0:
temp += arr2
return temp
@run_time
def merge_sort(arr: list):
total = len(arr)
step = 2
while True:
for i in range(0, total, step):
arr[i:i + step] = merge(arr[i:i + step//2], arr[i + step//2:i + step])
step *= 2
if step > 2 * total:
return arr
arr = make_arr(20000)
merge_sort(arr)
# run_time is 0.10300588607788086
def merge_sort(S):
temp = []
if len(S) < 2:
return S
split = len(S) // 2
left = merge_sort(S[:split])
right = merge_sort(S[split:])
finale = temp + merge(left, right)
return finale
def merge(left, right):
holder = []
while len(left) > 0 and len(right) > 0:
if left[0] < right[0]:
holder.append(left[0])
del left[0]
elif left[0] > right[0]:
holder.append(right[0])
del right[0]
if len(left) > 0:
holder.extend(left)
elif len(right) > 0:
holder.extend(right)
return holder
def splitArray(s):
return s[:len(s)//2], s[len(s)//2:]
# the idea here is i+j should sum to n as you increment i and j,
# but once out of bound, the next item of a or b is infinity
# therefore, the comparison will always switch to the other array
def merge(a, b, n):
result = [0] * n
a = a + [float('inf')]
b = b + [float('inf')]
result = [0] * n
i, j = 0, 0
for k in range(0, n):
if a[i] < b[j]:
result[k] = a[i]
i+=1
else:
result[k] = b[j]
j+=1
return result
def mergeSort(items):
n = len(items)
baseCase = []
if n == 0:
return baseCase
if n == 1:
baseCase.append(items[0])
return baseCase
if n == 2:
if items[0] < items[1]:
baseCase.append(items[0])
baseCase.append(items[1])
return baseCase
else:
baseCase.append(items[1])
baseCase.append(items[0])
return baseCase
left, right = splitArray(items)
sortedLeft = mergeSort(left)
sortedRight = mergeSort(right)
return merge(sortedLeft,sortedRight,n)
# Driver code to test above
arr = [12, 11, 13, 5, 6, 7]
n = len(arr)
print ("Given array is")
for i in range(n):
print ("%d" %arr[i]),
arr = mergeSort(arr)
print ("\n\nSorted array is")
for i in range(n):
print ("%d" %arr[i]),