LeetCode 两数之和 Python

参考：1. 两数之和-Python-LeetCode

给定一个整数数组和一个目标值，找出数组中和为目标值的两个数。

你可以假设每个输入只对应一种答案，且同样的元素不能被重复利用。

示例:

给定 nums = [2, 7, 11, 15], target = 9

因为 nums[0] + nums[1] = 2 + 7 = 9
所以返回 [0, 1]

解法一：

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        result=[0,0]
        len_nums=len(nums)
        for i in range(len_nums):
            for j in range(i+1,len_nums):
                if nums[j]==target-nums[i]:
                    result=[i,j]
                    break
                else:
                    continue
        if result!=[0,0]:
            return result[0],result[1]

解法二：

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        len_nums=len(nums)
        for i in range(len_nums):
            left=target-nums[i]
            if left in nums:
                index_of_left=nums.index(left)
                if i!=index_of_left:
                    return i,index_of_left

解法三：

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