# Time:  O(n)
# Space: O(n)
#
# Given an array of integers, find two numbers such that 
# they add up to a specific target number.
# The function twoSum should return indices of the two numbers such that
# they add up to the target, 
# where index1 must be less than index2. Please note that 
# your returned answers (both index1 and index2) are not zero-based.
# You may assume that each input would have exactly one solution.
#
# Input: numbers={2, 7, 11, 15}, target=9
# Output: index1=1, index2=2
#

class Solution:
    def twoSum(self, nums, target):
        lookup = {}
        for i, num in enumerate(nums):
            if target - num in lookup:
                return (lookup[target - num] + 1, i + 1)
            lookup[num] = i

if __name__ == '__main__':
    print "index1=%d, index2=%d" % Solution().twoSum((2, 7, 11, 15), 9)
# 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
        return []


if __name__ == '__main__':
    print "index1=%d, index2=%d" % Solution().twoSum((2, 7, 11, 15), 9)

Update two-sum.py