python学习思路三

1：回文数
思路，将数字转换为字符串，利用字符串的方法，将其翻转来达到效果，我喜欢用最简单的方法，

class Solution:
    def isPalindrome(self, x: int) -> bool:
        s=str(x)
        if s[::-1]== s:
            return  True
        else:
            return False

s=Solution()
x=123
print(s.isPalindrome(x))

#罗马数字转换

class Solution(object):
    def romanToInt(self, s):
        """
        :type s: str
        :rtype: int
        """
        d = {'I': 1, 'IV': 3, 'V': 5, 'IX': 8, 'X': 10, 'XL': 30, 'L': 50, 'XC': 80, 'C': 100, 'CD': 300, 'D': 500,
         'CM': 800, 'M': 1000}
        sum =0
        for i, n in enumerate(s):
            str1=s[max(i-1,0):i+1]
            if str1 in d:
                sum+=d.get(str1)
            else:
                sum+=d[n]
        return sum

1的个数

def hanmingWeight(n:int):
    m=0
    #利用bin函数将数字转换为二进制，同时转换为字符串
    for i in range(len(bin(n))):
        if bin(n)[i]=='1':
            m+=1
    return m

print(hanmingWeight(78))

#查找字符串中最长的个数
先根据长度排序，找出最短的字符串，
再进行循环对比

def longesCommonPrefix(strs):
    strs=sorted(strs,key=len)
    str1=strs[0]
    for i  in range(len(str1)):
        result=str1[0:i+1]
        j=0
        for j in range(len(strs)):
            if (strs[j][0:i+1]!=result):
                return str1[0:i]
    return  result
strs=["abc",'abd','abe']
print(longesCommonPrefix(strs))

一种更加简单的解法，直接让最短的和最长的比较

def longestCommonPrefix(strs):
    if not strs:
        return ""
    s1 = min(strs)
    s2 = max(strs)
    for i, x in enumerate(s1):
        if x != s2[i]:
            return s2[:i]
    return s1
print(type(longestCommonPrefix(strs)))

#杨辉三角用二维数组解决

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        ret=list()
        for i in range(numRows):
            row=list()
            for j in range(0,i+1):
                if j==0 or j==i:
                    row.append(1)
                else:
                    row.append(ret[i-1][j]+ret[i-1][j-1])
            ret.append(row)
        return ret

class Solution:
def searchInsert(self, nums: List[int], target: int) -> int:

    if target in nums:
        return nums.index(target)
    else:
        nums.append(target)
        nums.sort()
        return nums.index(target)

加1

def addone(nums):
s=‘’
l=[]
for i in nums:
s+=str(i) 将数字加入到字符串里面去
s=int(s) 转换成为数字
s+=1 加上1
s=str(s) 再转换成为字符串
for i in s:
l.append(int(i))将字符串里面的转回空列表
return l