字符串和哈希表(Python)

诈胡艺术 2020-11-13 03:19:53
Python 字符 字符串 哈希


目录

字符串:

Trie树:

朴素的字符串匹配算法:

相关练习:

哈希表:

LRU缓存淘汰算法:

相关练习:


字符串:

Trie树:

class Trie(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.root = {}
self.end = '/'
def insert(self, word): #插入
"""
Inserts a word into the trie.
:type word: str
:rtype: None
"""
node = self.root
for c in word:
if c not in node:
node[c] = {}
node = node[c]
node[self.end] = None
def search(self, word):#查找
"""
Returns if the word is in the trie.
:type word: str
:rtype: bool
"""
node = self.root
for c in word:
if c not in node:
return False
node = node[c]
if self.end in node:
return True
else:
return False
def startsWith(self, prefix):#前缀
"""
Returns if there is any word in the trie that starts with the given prefix.
:type prefix: str
:rtype: bool
"""
node = self.root
for c in prefix:
if c not in node:
return False
node = node[c]
return Tru

朴素的字符串匹配算法:

#朴素匹配
def matchStr(strs,substrs):
i = 0
j = 0
if not substrs:
return True
if not strs:
return False
while i<len(strs) and j<len(substrs):
print 'str: ',strs[i]
print 'substr: ',substrs[j]
if strs[i]==substrs[j]:
i += 1
j += 1
else:
i = i-j+1
j = 0
if j >= len(substrs):
return True
return False
#测试
a = "asdefvgty"
b = "vgt"
print matchStr(a,b)

相关练习:

反转字符串

编写一个函数,其作用是将输入的字符串反转过来。输入字符串以字符数组 char[] 的形式给出。

class Solution(object):
def reverseString(self, s):
"""
:type s: List[str]
:rtype: None Do not return anything, modify s in-place instead.
"""
l = len(s)
if l<=1:
return
for i in range(l/2):
s[i],s[l-1-i] = s[l-1-i],s[i]

翻转字符串里的单词

给定一个字符串,逐个翻转字符串中的每个单词。

class Solution(object):
def reverseWords(self, s):
"""
:type s: str
:rtype: str
"""
if not s:
return ""
s_list = s.split(' ')
ret_list = [i for i in s_list if i != '']
ret_list = ret_list[::-1]
return ' '.join(ret_list)

字符串转换整数 (atoi)

首先,该函数会根据需要丢弃无用的开头空格字符,直到寻找到第一个非空格的字符为止。

当我们寻找到的第一个非空字符为正或者负号时,则将该符号与之后面尽可能多的连续数字组合起来,作为该整数的正负号;假如第一个非空字符是数字,则直接将其与之后连续的数字字符组合起来,形成整数。

class Solution(object):
def myAtoi(self, str):
"""
:type str: str
:rtype: int
"""
s = str.strip()
ret =''
if len(s)<1:
return 0
if s[0]=='-' or s[0]=='+':#负号
if len(s)<=1 or not s[1].isdigit():
return 0
else:
ret += s[0]
for i in range(1,len(s)):
if s[i].isdigit():
ret += s[i]
else:
break
elif not s[0].isdigit():#字母
return 0
else:#数字
for i in range(0,len(s)):
if s[i].isdigit():
ret += s[i]
else:
break
num = int(ret)
if num>2**31-1:
return 2**31-1
elif num<-2**31:
return -2**31
else:
return num

 

哈希表:

LRU缓存淘汰算法:

from collections import OrderedDict
class LRU():
def __init__(self,capacity = 10):
self.maxcount = capacity
self.queue = OrderedDict()
def get(self,key):
if key not in self.queue:
return -1
else:
value = self.queue.pop(key)
self.queue[key] = value
return value
def put(self,key,data):
if key in self.queue:
self.queue.pop(key)
self.queue[key] = data
else:
if len(self.queue.items()) == self.maxcount:
self.queue.popitem(last = False)
self.queue[key] = data
else:
self.queue[key] = data

相关练习:

两数之和

给定一个整数数组 nums 和一个目标值 target,请你在该数组中找出和为目标值的那 两个 整数,并返回他们的数组下标

class Solution(object):
def twoSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
mydict = {}
for i in range(len(nums)):
if target-nums[i] in mydict:
return [mydict[target-nums[i]],i]
else:
mydict[nums[i]] = i

快乐数

编写一个算法来判断一个数是不是“快乐数”。

一个“快乐数”定义为:对于一个正整数,每一次将该数替换为它每个位置上的数字的平方和,然后重复这个过程直到这个数变为 1,也可能是无限循环但始终变不到 1。如果可以变为 1,那么这个数就是快乐数。

class Solution(object):
def isHappy(self, n):
"""
:type n: int
:rtype: bool
"""
history = []
while n>=10:
print 'n-:',n
sumnow = 0
m = 0
while n>=10:
m = n%10
n = n/10
sumnow += m*m
sumnow += n*n
n = sumnow
print 'n+:',n
return n == 1 or n == 7

 

版权声明
本文为[诈胡艺术]所创,转载请带上原文链接,感谢
https://blog.csdn.net/m0_38019841/article/details/88356378

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