two-sum-ii-input-array-is-sorted.py

# Time:  O(n)
# Space: O(1)
#
# Given an array of integers that is already sorted in ascending order, 
# 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):
        start, end = 0, len(nums) - 1
        
        while start != end:
            sum = nums[start] + nums[end]
            if sum > target:
                end -= 1
            elif sum < target:
                start += 1
            else:
                return [start + 1, end + 1]

if __name__ == "__main__":
    print Solution().twoSum([2, 7, 11, 15], 9)