python开发之常见算法

Posted 2020-12-25 Mr.Hui

二分查找

def bin_search(data_set, val):
    low = 0
    high = len(data_set) - 1

    while low <= high:
        mid = (low + high)//2
        if data_set[mid]==val:
            return mid
        elif data_set[mid] < val:
            low = mid + 1
        else:
            high = mid - 1

data = [1,4,2,5,63,4]
res = bin_search(data,63)
print(res)

冒泡排序

思路：首先列表中每两个相邻的数，如果前边的比后面的大，那么交换这两个数。

import random

def bubble_sort(list1):
    for i in range(len(list1)-1):
        for j in range(len(list1)-i-1):
            if list1[j]>list1[j+1]:
                list1[j],list1[j+1] = list1[j+1],list1[j]
data = list(range(15))
random.shuffle(data) #[2, 3, 13, 0, 14, 12, 6, 1, 4, 8, 10, 7, 11, 9, 5]
print(data)
res = bubble_sort(data) #[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
print(data)

优化后

import random

def bubble_sort(list1):
    for i in range(len(list1)-1):
        exchange = False
        for j in range(len(list1)-i-1):
            if (list1[j])>(list1[j+1]):
                list1[j],list1[j+1] = list1[j+1],list1[j]
                exchange = True
        if not exchange:
            break
data = list(range(20))
random.shuffle(data)
print(data) # [5, 1, 14, 13, 6, 15, 7, 12, 2, 16, 11, 9, 18, 8, 17, 3, 4, 10, 0, 19]
bubble_sort(data)
print(data) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

选择排序

思路：一趟遍历记录最小的数，放到第一个位置，再一趟遍历记录剩余列表中的最小的值，依次放置

import random
def select_sort(li):
    for i in range(len(li) - 1):
        min_loc = i
        for j in range(i+1,len(li)):
            if li[j]<li[min_loc]:
                min_loc = j
        li[i],li[min_loc] = li[min_loc],li[i]
data = list(range(20))
random.shuffle(data)
print(data)
select_sort(data)
print(data)

插入排序

import random
def insert_sort(li):
    for i in range(1,len(li)):
        temp = li[i]
        j = i - 1
        while j>=0 and li[j]>temp:
            li[j+1] = li[j]
            j = j-1
        li[j+1] = temp

data = list(range(20))
random.shuffle(data)
print(data)
insert_sort(data)
print(data)

快排

思路：1、取一个元素p（第一个元素）,使元素p归位

           2、列表被p分成两部分，左边都比p小，右边都比p大

           3、递归完成排序

总结：跟着我，右手左手一个慢动作，右手左手慢动作重播

def quick_sort(data,left,right):
    if left < right:
        mid = partition(data,left,right)
        quick_sort(data,left,mid - 1)
        quick_sort(data,mid+1,right)

def partition(data,left,right):
    tmp = data[left]
    while left < right:
        while left<right and data[right]>=tmp: # 右手
            right -= 1
        data[left] = data[right]
        while left<right and data[left]<=tmp: # 左手
            left += 1
        data[right] = data[left]
    data[left] = tmp
    return left
import random
data = list(range(20))
random.shuffle(data)
print(data) # [19, 4, 0, 7, 14, 8, 2, 12, 11, 17, 13, 3, 18, 10, 6, 1, 15, 5, 16, 9]
quick_sort(data,0,len(data)-1)
print(data) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]