> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Two Sum II - Input Array Is Sorted

> Tested Python solution for LeetCode 167 with 14 pytest cases. Generate a practice environment with lcpy.

LeetCode 167, Medium. Topics: Array, Two Pointers, Binary Search. [View on LeetCode](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/description/).

Generate this problem as a practice environment: tested reference solution, 14 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 167   # by problem number
lcpy gen -s two_sum_ii_input_array_is_sorted   # by problem name
```

## Problem

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`*, **each incremented 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.

### Examples

```
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].

```
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].

```
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 \* 10^4
* -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**.

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/two_sum_ii_input_array_is_sorted/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/two_sum_ii_input_array_is_sorted/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(1)
    def two_sum(self, numbers: list[int], target: int) -> list[int]:
        left, right = 0, len(numbers) - 1
        while left < right:
            current = numbers[left] + numbers[right]
            if current == target:
                return [left + 1, right + 1]
            if current < target:
                left += 1
            else:
                right -= 1
        return []
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(1)  |

## Tags

[NeetCode 150](/catalog/neetcode-150), [NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).