167.md

167. Two Sum II - Input array is sorted

难度: Easy

刷题内容

原题连接

• https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/description/

内容描述

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.

解题方案

思路 1 - 时间复杂度: O(lgN) - 空间复杂度: O(1)

二分法+双指针，beats 95.15%

因为答案唯一，符合要求return即可

class Solution(object):
    def twoSum(self, numbers, target):
        """
        :type numbers: List[int]
        :type target: int
        :rtype: List[int]
        """
        r, lens = 0, len(numbers) - 1
        while r < lens:
            if numbers[r] + numbers[lens] == target:
                return [r+1, lens+1]
            elif numbers[r] + numbers[lens] < target:
                r += 1
            else:
                lens -= 1

总结：

1. 此题和001题很类似，区别在与此题参数为有序数组，并且返回的index+1