Find a pair with target sum in a sorted array

Summary

Use the two-pointer technique to determine if any two numbers in a sorted array sum to a target.

Problem statement

Given a sorted list of integers (ascending) and a target integer, determine if there exists any pair of distinct elements in the list whose sum is equal to the target. Return True if such a pair exists, otherwise return False. Use the two-pointer technique to achieve O(n) time and O(1) extra space.

Task

Implement an efficient O(n) two-pointer solution that checks for a pair summing to a given target in a sorted list.

Examples

Input format

A sorted list of integers 'arr' and an integer 'target'. The function signature: pair_with_target(arr, target).

Output format

Return True if a pair exists that sums to target, otherwise False.

Constraints

0 <= len(arr) <= 10^5. Array is sorted in non-decreasing order. Aim for O(n) time and O(1) extra space.

Samples