[剑指Offer]最小的K个数[Python]

题目要求：数组中有一个数字出现的次数超过数组长度的一半，请找出这个数字。例如输入一个长度为9的数组{1,2,3,2,2,2,5,4,2}。由于数字2在数组中出现了5次，超过数组长度的一半，因此输出2。如果不存在则输出0。

解题思路：最简单的冒泡排序，当然不是最有答案，复杂度太大Ｏ（nk）

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution(self, tinput, k):
        res = []
        if tinput and k<=len(tinput):
            for i in range(k):
                jjend = len(tinput)-1
                for jj in range(jjend):
                    if tinput[jj] < tinput[jj+1]:
                        tinput[jj],tinput[jj+1] = tinput[jj+1],tinput[jj]
                res.append(tinput.pop())
            return res
        else:

            return []

看到牛友把好多种排序方法都实现了，膜拜一下，先复制下来，以后看一下：

链接：https://www.nowcoder.com/questionTerminal/6a296eb82cf844ca8539b57c23e6e9bf
来源：牛客网

方法一：蒂姆排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        if tinput = = [] or k > len (tinput):
            return []
        tinput.sort()
        return tinput[: k]

方法二：快速排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        def quick_sort(lst):
            if not lst:
                return []
            pivot = lst[ 0 ]
            left = quick_sort([x for x in lst[ 1 : ] if x < pivot])
            right = quick_sort([x for x in lst[ 1 : ] if x > = pivot])
            return left + [pivot] + right

        if tinput = = [] or k > len (tinput):
            return []
        tinput = quick_sort(tinput)
        return tinput[: k]

方法三：归并排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        def merge_sort(lst):
            if len (lst) < = 1 :
                return lst
            mid = len (lst) / / 2
            left = merge_sort(lst[: mid])
            right = merge_sort(lst[mid:])
            return merge(left, right)
        def merge(left, right):
            l, r, res = 0 , 0 , []
            while l < len (left) and r < len (right):
                if left[l] < = right[r]:
                    res.append(left[l])
                    l + = 1
                else :
                    res.append(right[r])
                    r + = 1
            res + = left[l:]
            res + = right[r:]
            return res
        if tinput = = [] or k > len (tinput):
            return []
        tinput = merge_sort(tinput)
        return tinput[: k]

方法四：堆排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        def siftup(lst, temp, begin, end):
            if lst = = []:
                return []
            i, j = begin, begin * 2 + 1
            while j < end:
                if j + 1 < end and lst[j + 1 ] > lst[j]:
                    j + = 1
                elif temp > lst[j]:
                    break
                else :
                    lst[i] = lst[j]
                    i, j = j, 2 * j + 1
            lst[i] = temp

        def heap_sort(lst):
            if lst = = []:
                return []
            end = len (lst)
            for i in range ((end / / 2 ) - 1 , - 1 , - 1 ):
                siftup(lst, lst[i], i, end)
            for i in range (end - 1 , 0 , - 1 ):
                temp = lst[i]
                lst[i] = lst[ 0 ]
                siftup(lst, temp, 0 , i)
            return lst

        if tinput = = [] or k > len (tinput):
            return []
        tinput = heap_sort(tinput)
        return tinput[: k]

方法五：冒泡排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        def bubble_sort(lst):
            if lst = = []:
                return []
            for i in range ( len (lst)):
                for j in range ( 1 , len (lst) - i):
                    if lst[j - 1 ] > lst[j]:
                        lst[j - 1 ], lst[j] = lst[j], lst[j - 1 ]
            return lst

        if tinput = = [] or k > len (tinput):
            return []
        tinput = bubble_sort(tinput)
        return tinput[: k]

方法六：直接选择排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        def select_sort(lst):
            if lst = = []:
                return []
            for i in range ( len (lst) - 1 ):
                smallest = i
                for j in range (i, len (lst)):
                    if lst[j] < lst[smallest]:
                        smallest = j
                lst[i], lst[smallest] = lst[smallest], lst[i]

            return lst

        if tinput = = [] or k > len (tinput):
            return []
        tinput = select_sort(tinput)
        return tinput[: k]

方法七：插入排序

# -*- coding:utf-8 -*-
class Solution:
    def GetLeastNumbers_Solution( self , tinput, k):
        # write code here
        def Insert_sort(lst):
            if lst = = []:
                return []
            for i in range ( 1 , len (lst)):
                temp = lst[i]
                j = i
                while j > 0 and temp < lst[j - 1 ]:
                    lst[j] = lst[j - 1 ]
                    j - = 1
                lst[j] = temp
            return lst

        if tinput = = [] or k > len (tinput):
            return []
        tinput = Insert_sort(tinput)
        return tinput[: k]