算法图解--读书笔记

一、二分法查找：适用于有序的列表查找想要的元素。

• 操作对象：数组
• 使用前提：有序的数组
• 性能方面：时间复杂度O(logn)

# -*- coding: utf-8 -*-

def binary_search(list, item):
    low = 0
    high = len(list) - 1
    sequence = 0
    while low <= high:
        mid = int((low + high) / 2)  #这里必须是整数
        guess = list[mid]
        sequence += 1
        if guess == item:
            print('sequence', sequence)
            return mid
        if guess > item:
            high = mid - 1
        else:
            low = mid + 1
    return None


list1 = range(129)
list2 = range(10000009)
print('index', binary_search(list1, 23))
print('index2', binary_search(list2, 2))

二、比较排序法：适用与数字之间的排序

     2.1 选择排序：将数组元素按照从小到大的顺序排序，每次从数组中取出最小值

     2.2、数组和链表

            数组：连续存储在硬盘中；链表：分散存储在硬盘中；

def findsmallest(arr):
    smallest = arr[0]
    smallest_index = 0
    for i in range(1, len(arr)):
        if arr[i] < smallest:
            smallest = arr[i]
            smallest_index = i
    return smallest_index


def selectionsort(arr):
    newarr = []
    for i in range(len(arr)):
        smallest = findsmallest(arr)
        newarr.append(arr.pop(smallest))
    return newarr

print (selectionsort([1,2,3,2,2,2,234,3421,334,2343,443,52]))