python 算法

本文参考老男孩视屏

算法

一个计算过程,解决问题的方法

输入-->算法-->输出

递归

• 调用自身
• 结束条件

时间复杂度

O(1)

print('hello word')

O(n2)

for i in range(n):
    for l in range(n):

O(n3)

for i in range(n):
    for l in range(n):
        for k in range(n):

O(logn)

while n>0:
    n//2

总结

时间复杂用来估计一个算法运行式子

O(1)<O(logn)<O(n)<O(nlogn)<O(n2)<O(n2logn)<O(n3)

空间复杂度

列表查找

顺序查找 O(n)

def linear_search(data_set, value): 
    for i in  range(range(data_set)):
        if data_set[i] == value:
        return i
    return

二分查找 (logn)

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
        return

bin_search()

排序:

冒泡排序(bubble_sort)

选个开始一个数,通过交换把一个大的数选出来,便利一趟可以选出一个最大的数据,

import random,time

def func_time(func):
    def wapper(*args,**kwargs):
        time_start =time.time()
        x = func(*args,**kwargs)
        time_stop = time.time() -time_start
        print("time cost:",time_stop)
        return x
    return wapper

@func_time
def bubble_sort(li):
    for i in range(len(li) - 1):
        exchange = False
        for k in range(len(li) - i - 1):
             if li[k] > li[k+1]:
                 li[k],li[k+1] = li[k+1],li[k]
                 exchange = True
        if not exchange:
            break

data = list(range(10000))
random.shuffle(data)

bubble_sort(data)
print(data)