数据结构与算法例题(4)——哈希表

#第一种方法：直接判断集合长度
class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        len1=len(nums)
        len2=len(set(nums))
        if len1==len2:
            return False
        else:
            return True
#2.使用hash表
        #首先判断元素长度是否为0
        if len(nums)==0:
            return False
        hashtable={}
        for num in nums:
            if num not in hashtable.keys():
                hashtable[num]=1
            else:
                #当需要得到次数时用这个
                # temp=hashtable.values
                # hashtable[num]=temp+1
                return True
        return False

#统计两个字符串中元素出现的个数 自己写的还是很复杂
class Solution:
    def findTheDifference(self, s: str, t: str) -> str:
        hashtable1={}
        hashtable2={}
        for i in s:
            if i not in hashtable1.keys():
                hashtable1[i]=1
            else:
                temp=hashtable1[i]
                hashtable1[i]=temp+1
        for j in t:
            if j not in hashtable2.keys():
                hashtable2[j]=1
            else:
                temp=hashtable2[j]
                hashtable2[j]=temp+1
        for key1 in hashtable1.keys():
            for key2 in hashtable2.keys():
                if key1==key2:
                    hashtable2[key2]=hashtable2[key2]-hashtable1[key1]
        for keys,values in hashtable2.items():
            if values!=0:
                return keys