[LeetCode] 167. Two Sum II - Input array is sorted_Easy tag: Hash/Two pointers

 

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.

Example:

Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.

这个题目还是可以像[LeetCode] 1. Two Sum_Easy tag: Hash Table 用Hash table去做，T: O(n)   S: O(n)

不过因为题目已经给了sorted array，所以可以用two pointers 去将S: 降为 O(1)

Code

class Solution:
    def twoSum2(self, nums, target):
        left, right = 0, len(nums) - 1
        while left < right:
            total = nums[left] + nums[right]
            if total == target:
                return [left + 1, right + 1]
            elif total < target:
                left += 1
            else:
                right -= 1