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.

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• 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

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• 返回： index

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

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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。

这里用dict解法。

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 []