常见的查找算法的原理及python实现

Posted 2020-11-02 水如如

• 顺序查找
• 二分查找
• 练习

---

一、顺序查找

data=[1,3,4,5,6]
value=1
def linear_search(data,value):
    flag=False
    for i in range(0,len(data)):
        if data[i]==value:
            # return i
            flag=True
            print(\'找到了，在第%s个位置\'%i)
    if not flag:
        print(\'查找失败\')
# linear_search(data,value)

二、二分查找

递归：（效率不高）

递归需要有结束条件（len(data)<=1）,每一次递归的问题规模都减小

改变的是每次传入的data

#递归实现
def bin_search2(data,value):
    mid=len(data)/2
    if len(data)>1:
        if value>data[mid]:
            bin_search2(data[mid+1:],value)
        elif value<data[mid]:
            bin_search2(data[0:mid-1],value)
        else:
            return mid
    else:
        if data[0]==value:
            return 0
        else:
            print(\'查找失败\')

非递归：

改变的是low和high指针的指向

def bin_search(data,value):
     flag=False
     low=0
     high=len(data)-1
     while low<=high:
         mid=(low+high)//2
         if value>data[mid]:
             low=mid+1
         elif value<data[mid]:
             high=mid-1
         else:
             flag=True
             return mid
     if not flag:
         print(\'查找失败\')
print(bin_search(data,value))

三、练习

#练习
info=[
    {"id":1001, "name":"张三", "age":20},
    {"id":1002, "name":"李四", "age":25},
    {"id":1004, "name":"王五", "age":23},
    {"id":1007, "name":"赵六", "age":33}
]
def bin_search(data,value):
    low=0
    high=len(data)-1
    while low<=high:
        mid=(low+high)//2
        if data[mid][\'id\']==value:#取字典的value 用dic[key]
            return (mid,data[mid])
        elif data[mid][\'id\']<value:
            low=mid+1
        else:
            high=mid-1
    else:
        return (0,None)#根据返回值判断是否查到这个人

while True:
    id=int(input(\'请输入需要查找的学号（退出请按Q）:\').strip())
    # print(type(id))
    if id==\'q\':
        break
    else:
        num,info=bin_search(info,id)
        if info==\'None\':
            print(\'查无此人\')
        else:
            print(\'info:%s\'%info)