leetcode 167 two sum II

167. Two Sum II - Input array is sorted

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.

双指针问题，由于是排过序的列表，可以左指针指向起始，右指针指向末尾。两个指针根据条件收缩。最终找到符合的两个值。

如果numbers[left] + numbers[right] 大于target，则右指针左移，使和减小。

如果numbers[left] + numbers[right] 小于target，则左指针右移，使和增大。

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

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