Python 目标。 def select(L): if len(L) < 10: L.sort() return L[int(len(L)/2)] S = [] lIndex = 0 while l

目标。

def select(L):
    if len(L) < 10:
        L.sort()
        return L[int(len(L)/2)]
    S = []
    lIndex = 0
    while lIndex+5 < len(L)-1:
        S.append(L[lIndex:lIndex+5])
        lIndex += 5
    S.append(L[lIndex:])
    Meds = []
    for subList in S:
        print(subList)
    Meds.append(select(subList))
    L2 = select(Meds)
    L1 = L3 = []
    for i in L:
        if i < L2:
            L1.append(i)
        if i > L2:
            L3.append(i)
    if len(L) < len(L1):
        return select(L1)
    elif len(L) > len(L1) + 1:
        return select(L3)
    else:
        return L2

L = list(range(100))
shuffle(L)
print(select(L))

def select(L):
    if len(L) < 10:
        L.sort()
        return L[int(len(L)/2)]
    S = []
    lIndex = 0
    while lIndex+5 < len(L)-1:
        S.append(L[lIndex:lIndex+5])
        lIndex += 5
    S.append(L[lIndex:])
    Meds = []
    for subList in S:
        print(subList)
        Meds.append(select(subList))
    L2 = select(Meds)
    L1 = L3 = []
    for i in L:
        if i < L2:
            L1.append(i)
        if i > L2:
            L3.append(i)
    if len(L) < len(L1):
        return select(L1)
    elif len(L) > len(L1) + 1:
        return select(L3)
    else:
        return L2

def select(L, j):
    if len(L) < 10:
        L.sort()
        return L[j]
    S = []
    lIndex = 0
    while lIndex+5 < len(L)-1:
        S.append(L[lIndex:lIndex+5])
        lIndex += 5
    S.append(L[lIndex:])
    Meds = []
    for subList in S:
        Meds.append(select(subList, int((len(subList)-1)/2)))
    med = select(Meds, int((len(Meds)-1)/2))
    L1 = []
    L2 = []
    L3 = []
    for i in L:
        if i < med:
            L1.append(i)
        elif i > med:
            L3.append(i)
        else:
            L2.append(i)
    if j < len(L1):
        return select(L1, j)
    elif j < len(L2) + len(L1):
        return L2[0]
    else:
        return select(L3, j-len(L1)-len(L2))

#!/bin/python
#
# TH @stackoverflow, 2016-01-20, linear time "median of medians" algorithm
#
import sys, random


items_per_column = 15


def find_i_th_smallest( A, i ):
    t = len(A)
    if(t <= items_per_column):
        # if A is a small list with less than items_per_column items, then:
        #     1. do sort on A
        #     2. return the i-th smallest item of A
        #
        return sorted(A)[i]
    else:
        # 1. partition A into columns of items_per_column items each. items_per_column is odd, say 15.
        # 2. find the median of every column
        # 3. put all medians in a new list, say, B
        #
        B = [ find_i_th_smallest(k, (len(k) - 1)/2) for k in [A[j:(j + items_per_column)] for j in range(0,len(A),items_per_column)]]

        # 4. find M, the median of B
        #
        M = find_i_th_smallest(B, (len(B) - 1)/2)

        # 5. split A into 3 parts by M, { < M }, { == M }, and { > M }
        # 6. find which above set has A's i-th smallest, recursively.
        #
        P1 = [ j for j in A if j < M ]
        if(i < len(P1)):
            return find_i_th_smallest( P1, i)
        P3 = [ j for j in A if j > M ]
        L3 = len(P3)
        if(i < (t - L3)):
            return M
        return find_i_th_smallest( P3, i - (t - L3))


# How many numbers should be randomly generated for testing?
#
number_of_numbers = int(sys.argv[1])


# create a list of random positive integers
#
L = [ random.randint(0, number_of_numbers) for i in range(0, number_of_numbers) ]


# Show the original list
#
print L


# This is for validation
#
print sorted(L)[int((len(L) - 1)/2)]


# This is the result of the "median of medians" function.
# Its result should be the same as the validation.
#
print find_i_th_smallest( L, (len(L) - 1) / 2)