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# 167. Two Sum II - Input Array Is Sorted

Medium
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.
Your solution must use only constant extra space.
Example 1:
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. We return [1, 2].
Example 2:
Input: numbers = [2,3,4], target = 6
Output:
[1,3]
Explanation:
The sum of 2 and 4 is 6. Therefore index1 = 1, index2 = 3. We return [1, 3].
Example 3:
Input: numbers = [-1,0], target = -1
Output:
[1,2]
Explanation:
The sum of -1 and 0 is -1. Therefore index1 = 1, index2 = 2. We return [1, 2].
Constraints:
• `2 <= numbers.length <= 3 * 104`
• `-1000 <= numbers[i] <= 1000`
• `numbers` is sorted in non-decreasing order.
• `-1000 <= target <= 1000`
• The tests are generated such that there is exactly one solution.

### 解題

func twoSum(numbers []int, target int) []int {
left := 0
right := len(numbers) - 1
for left < right {
sum := numbers[left] + numbers[right]
if sum == target {
return []int{left + 1, right + 1}
} else if sum < target {
left++
} else {
right--
}
}
return []int{left+1, right+1}
}