---
title: "ByteByteGo: Pair Sum - Sorted"
url: https://perrotta.dev/2025/11/bytebytego-pair-sum-sorted/
last_updated: 2026-02-16
---


[ByteByteGo: Pair Sum — Sorted](https://bytebytego.com/exercises/coding-patterns/two-pointers/pair-sum-sorted):

```python
from typing import List

def pair_sum_sorted(nums: List[int], target: int) -> List[int]:
    left = 0
    right = len(nums) - 1

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

    return []
```

Classic Two Pointer problem, inward traversal.

In a single pass:

```python
from typing import List

def pair_sum_unsorted(nums: List[int], target: int) -> List[int]:
    d = {}
    for i, num in enumerate(nums):
        if (target - num) in d.keys():
            return [d[target-num], i]
        d[num] = i

    return []
```