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))