两数之和（1）

法一：

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        ret = []
        for i in range(len(nums)):
            for j in range(1,len(nums)-i):
                if nums[i] + nums[-j] == target:
                    ret.append(i)
                    ret.append(len(nums)-j)
                    return re

法二：

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
    
         hashmap = {}
        for ind, num in enumerate(nums):
            hashmap[num] = ind
        for i, num in enumerate(nums):
            j = hashmap.get(target - num)
            if j is not None and i != j:
                return [i, j]
法三：

class Solution(object):

    def twoSum(self, nums, target):

        ret = []

        for i in nums:

            other = target-i

            current_index = nums.index(i)

            if other in nums[current_index+1:]:

                other_index = nums[current_index+1:].index(other)

                ret.append(current_index)

                ret.append(current_index+other_index+1)

                break

        return ret