Count Pairs with Sum

You are given an array of integers and a target integer \(T\). Your task is to determine the number of pairs \( (i, j)\) with \(i < j\) such that the sum of the elements at positions \(i\) and \(j\) equals \(T\). In mathematical terms, find the number of pairs satisfying \(a_i + a_j = T\). Note that when identical numbers appear multiple times, each distinct pair is counted. For instance, if the array is [1, 2, 3, 4] and \(T=5\), there are 2 valid pairs: (1,4) and (2,3).

inputFormat

The input is read from stdin and consists of two lines. The first line contains two integers \(n\) and \(T\), where \(n\) is the number of elements in the array and \(T\) is the target sum. The second line contains \(n\) space-separated integers representing the array elements.

outputFormat

Output a single integer to stdout which is the count of all pairs \( (i, j)\) such that \(a_i + a_j = T\) and \(i < j\).

3 7
1 2 3

0