Find Pair Given Difference.cpp

/*
Find Pair Given Difference
==========================

Given an unsorted array Arr[] and a number N. You need to write a program to find if there exists a pair of elements in the array whose difference is N.

Input:
First line of input contains an integer T which denotes the number of test cases. Then T test cases follows. First line of each test case contains two space separated integers L and N where L denotes the length of array or the number of elements in the array and N denotes the difference between two elements. Second line of each test case contains L space separated integers which denotes the elements of the array.

Output:
For each test case, in a new line print 1 if the pair is found otherwise print -1 if there does not exist any such pair.

Constraints:
1<=T<=100
1<=L<=104
1<=Arr[i]<=105

Example:
Input:
2
6 78
5 20 3 2 5 80
5 45
90 70 20 80 50
Output:
1
-1
*/

#include <bits/stdc++.h>
using namespace std;

int solve()
{
  int l, n;
  cin >> l >> n;
  vector<int> arr(l, 0);
  for (auto &i : arr)
    cin >> i;

  unordered_set<int> s;
  for (auto &i : arr)
  {
    if (s.find(abs(n - i)) != s.end() || s.find(n + i) != s.end())
      return 1;
    else
      s.insert(i);
  }

  return -1;
}

int main()
{
  int t;
  cin >> t;
  while (t--)
  {
    cout << solve() << endl;
  }
  return 0;
}