two-sum.py

# Time:  O(n)
# Space: O(n)

# 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.
#
# Example:
# Given nums = [2, 7, 11, 15], target = 9,
#
# Because nums[0] + nums[1] = 2 + 7 = 9,
# return [0, 1].


class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        lookup = {}
        for i, num in enumerate(nums):
            if target - num in lookup:
                return [lookup[target - num], i]
            lookup[num] = i

    def twoSum2(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        for i in nums:
            j = target - i
            tmp_nums_start_index = nums.index(i) + 1
            tmp_nums = nums[tmp_nums_start_index:]
            if j in tmp_nums:
                return [nums.index(i), tmp_nums_start_index + tmp_nums.index(j)]


if __name__ == '__main__':
    print(Solution().twoSum((2, 7, 11, 15), 9))
    print(Solution().twoSum2((2, 7, 11, 15), 9))