Two Sum II - Input Array Is Sorted

LeetCode

Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length.

Return the indices of the two numbers, index1 and index2, added by one as an integer array [index1, index2] of length 2.

The tests are generated such that there is exactly one solution. 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.
1def twoSum(numbers: List[int], target: int) -> List[int]:
2    l, r = 0, len(numbers) - 1
3    
4    while l < r:
5        curSum = numbers[l] + numbers[r]
6        
7        if curSum > target:
8            r -= 1
9        elif curSum < target:
10            l += 1
11        else:
12            return [l + 1, r + 1]
13    return []
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l
2
0
7
1
11
2
r
15
3
target=9
Step 1 / 4
Step 1:
Initialize pointers l=0, r=3. Target is 9.
Pointers: l=0, r=3
Focus: select @ [0, 3]
target=9