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.

  • 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]


  • 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 []