# 167 Two Sum II - Input array is sorted

Original Description: 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.
Note:

• Your returned answers (both index1 and index2) are not zero-based.
• You may assume that each input would have exactly one solution and you may not use the same element twice.

• 要求： 给一个有序数组，和一个target, 返回其中两个和为target的元素的位置 (index)。
• note: 数组index不是从0开始的

• 返回： index

• 例子：
• input: [2,7,11,15], target = 9
• output: [1,2]

## Solution

• 可以用与 001 Two Sum 相同的解法， 即用dict保存元素坐标，判断目标和减去当前值 是否在dict中， 有则返回坐标，无则存储当前元素:坐标。
• 由于序列有序，可以使用两个指针从两边向中间逼近。

class Solution:
def twoSum(self, nums, target):
"""
:type numbers: List[int]
:type target: int
:rtype: List[int]
"""

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