[LeetCode] Challenge log 167

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167. Two Sum II - Input array is sorted

Same as #1, #653. Either use set or 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:

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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.
Soulution:
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class Solution(object):
    def twoSum(self, numbers, target):
        """
        :type numbers: List[int]
        :type target: int
        :rtype: List[int]
        """
        l = 0
        r = len(numbers) - 1
        while l < r:
            s = numbers[l] + numbers[r]
            if  s == target:
                return [l+1, r+1]
            elif s < target:
                l += 1
            else:
                r -= 1
        return None
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