# LeetCode 167: Two Sum Ii Input Array Is Sorted — Step-by-Step Visual Trace

**Medium** — Two Pointers | Array | Binary Search

## The Problem

Find two numbers in a sorted array that add up to a specific target value, returning their 1-indexed positions.

## Approach

Use two pointers starting from opposite ends of the sorted array. Move the left pointer right if the sum is too small, or move the right pointer left if the sum is too large, leveraging the sorted property to efficiently narrow down the search space.

**Time:** O(n) · **Space:** O(1)

## Code

```python
class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        left, right = 0, len(numbers) - 1

        while left < right:
            current_sum = numbers[left] + numbers[right]

            if current_sum == target:
                return [left + 1, right + 1]
            elif current_sum < target:
                left += 1
            else:
                right -= 1

        # No solution found
        return [-1, -1]
```

## Watch It Run

> **[Open interactive visualization](https://tracelit.dev/app?trace=0167_two-sum-ii-input-array-is-sorted)**

> **Try it yourself:** Open [TraceLit](https://tracelit.dev/app?trace=0167_two-sum-ii-input-array-is-sorted) and step through every line.

---

*Built with [TraceLit](https://tracelit.dev) — the visual algorithm tracer for LeetCode practice.*