leetcode1 twoSum

 """
 Given an array of integers, return indices of the two numbers such that they add up to a specific target.

 You may assume that each input would have exactly one solution, and you may not use the same element twice.

 Example:

 Given nums = [2, 7, 11, 15], target = 9,

 Because nums[0] + nums[1] = 2 + 7 = 9,
 return [0, 1].

 """

 """
 第一种是思路简单的方法，先遍历求出目标值，再遍历目标值是否再数组中，
 判断如果下标相等则继续，最后返回[i,j]
 """
 class Solution1(object):
     def twoSum(self, nums, target):
         n = len(nums)
         for i in range(n):
             a = target - nums[i]
             if (a in nums):       #这里其实隐含了一层循环
                 j = nums.index(a)
                 if (i==j):
                     continue
                 else:
                     return [i,j]
                     break
             else:
                 continue
 """
 第二种方法用了dict查找，提高效率
 enumerate函数用法：
 seasons = ['Spring', 'Summer', 'Fall']
 list(enumerate(seasons))
 [(0, 'Spring'), (1, 'Summer'), (2, 'Fall')]
 """
 class Solution2(object):
     def twoSum(self, nums, target):
         dict = {}
         for i, num in enumerate(nums):
             if target - num in dict:
                 return [dict[target - num], i]
             else:
                 dict[num] = i
 nums = [2, 7, 11, 15]
 target = 9
 result1 = Solution1()
 result2 = Solution2()
 print(result1.twoSum(nums, target))
 print(result1.twoSum(nums, target))