TwoSum

"""复杂度O(n)"""
class Solution:
    def twoSum(self, nums, target):
        dict1={}
        for i in range(len(nums)):
            if nums[i] in dict1: #利用字典查找复杂度为O(1),而暴力解法问题就在每次比较复杂\n度依然为o(n)
                 return [dict1[nums[i]],i] #return满足刷题要求
            else:
                dict1[target-nums[i]] = i   #字典的赋值，dict[key]=valuw
if __name__ =="__main__":
    s=Solution()
    s.twoSum([2,7,11,15],9)
"""双指针"""
class Solution:
    def twoSum(self,nums,target):
        l=len(nums)
        array = list(zip(nums,range(l)))   #zip将两个列表按对应元素形成含多个元组的新列表
        array.sort()    #此时array已经改变了，但是内存位置也变了
        low=0
        high=l-1
        while low<high:
            S=array[low][0]+array[high][0]
            if S<target:
                low += 1
            elif S>target:
                high -= 1
            else:
                return [array[low][1],array[high][1]]