0167. Two Sum II - Input array is sorted.md

题目

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.

我的思路

由于数组是有序的，因此使用双指针，一个从头开始，一个从尾部开始，若和等于target则输出两个指针的位置；若和小于target则头指针向后移动一格；若和大于target则尾指针向前移动一格。

class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        a = 0
        b = len(numbers)-1
        while a < b:
            temp = numbers[a] + numbers[b]
            if temp == target:
                return (a+1,b+1)
            if temp < target:
                a += 1
            else:
                b -= 1