Pair with Sum

Given an array of integers and a target sum, determine whether there exists a pair of distinct elements in the array whose sum equals the target. If such a pair exists, output YES; otherwise, output NO. The intended solution should be efficient enough to handle larger inputs. Mathematically, if the array is \(a_1, a_2, \dots, a_n\) and the target is \(T\), you need to decide if there exists indices \(i, j\) with \(i \neq j\) such that \(a_i + a_j = T\).

inputFormat

The input is given in three lines:

• The first line contains an integer \(n\), denoting the number of elements in the array.
• The second line contains \(n\) space-separated integers, representing the array elements.
• The third line contains an integer, representing the target sum \(T\).

outputFormat

Output a single line with YES if there exists a pair of distinct elements whose sum equals the target; otherwise, output NO.

5
1 2 3 4 5
9

YES