# Pairs of Positive Negative values in an array

• Difficulty Level : Easy
• Last Updated : 17 Jan, 2022

Given an array of distinct integers, print all the pairs having positive value and negative value of a number that exists in the array. We need to print pairs in order of their occurrences. A pair whose any element appears first should be printed first.

Examples:

```Input  :  arr[] = { 1, -3, 2, 3, 6, -1 }
Output : -1 1 -3 3

Input  :  arr[] = { 4, 8, 9, -4, 1, -1, -8, -9 }
Output : -1 1 -4 4 -8 8 -9 9```

Method 1 (Simple : O(n2))
The idea is to use two nested loop. For each element arr[i], find negative of arr[i] from index i + 1 to n – 1 and store it in another array. For output, sort the stored element and print negative positive value of the stored element.

Below is the implementation of this approach:

## C++

 `// Simple CPP program to find pairs of positive``// and negative values present in an array.``#include ``using` `namespace` `std;` `// Print pair with negative and positive value``void` `printPairs(``int` `arr[], ``int` `n)``{``    ``vector<``int``> v;` `    ``// For each element of array.``    ``for` `(``int` `i = 0; i < n; i++)` `        ``// Try to find the negative value of``        ``// arr[i] from i + 1 to n``        ``for` `(``int` `j = i + 1; j < n; j++)` `            ``// If absolute values are equal print pair.``            ``if` `(``abs``(arr[i]) == ``abs``(arr[j]))``                ``v.push_back(``abs``(arr[i]));     ` `    ``// If size of vector is 0, therefore there is no``    ``// element with positive negative value, print "0"``    ``if` `(v.size() == 0)``       ``return``;` `    ``// Sort the vector``    ``sort(v.begin(), v.end());` `    ``// Print the pair with negative positive value.``    ``for` `(``int` `i = 0; i < v.size(); i++)``        ``cout << -v[i] << ``" "` `<< v[i];   ``}` `// Driven Program``int` `main()``{``    ``int` `arr[] = { 4, 8, 9, -4, 1, -1, -8, -9 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``printPairs(arr, n);``    ``return` `0;``}`

## Java

 `// Java program to find pairs of positive``// and negative values present in an array.``import` `java.util.*;``import` `java.lang.*;` `class` `GFG {` `    ``// Print pair with negative and positive value``    ``public` `static` `void` `printPairs(``int` `arr[] , ``int` `n)``    ``{``        ``Vector v = ``new` `Vector();``        ``// For each element of array.``        ``for` `(``int` `i = ``0``; i < n; i++)` `            ``// Try to find the negative value of``            ``// arr[i] from i + 1 to n``            ``for` `(``int` `j = i + ``1``; j < n; j++)` `                ``// If absolute values are equal``                ``// print pair.``                ``if` `(Math.abs(arr[i]) ==``                                  ``Math.abs(arr[j]))``                    ``v.add(Math.abs(arr[i]));`  `        ``// If size of vector is 0, therefore there``        ``// is no element with positive negative``        ``// value, print "0"``        ``if` `(v.size() == ``0``)``            ``return``;    ``    ` `        ``// Sort the vector``        ``Collections.sort(v);` `        ``// Print the pair with negative positive``        ``// value.``        ``for` `(``int` `i = ``0``; i < v.size(); i++)``            ``System.out.print(-v.get(i) + ``" "` `+``                                      ``v.get(i));``    ``}` `    ``// Driven Program``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `arr[] = { ``4``, ``8``, ``9``, -``4``, ``1``, -``1``, -``8``, -``9` `};``        ``int` `n = arr.length;``        ``printPairs(arr, n);``    ``}``}` `// This code is contributed by Prasad Kshirsagar.`

## Python 3

 `# Simple Python 3 program to find``# pairs of positive and negative``# values present in an array.` `# Print pair with negative and``# positive value``def` `printPairs(arr, n):``    ``v ``=` `[]` `    ``# For each element of array.``    ``for` `i ``in` `range``(n):` `        ``# Try to find the negative value``        ``# of arr[i] from i + 1 to n``        ``for` `j ``in` `range``( i ``+` `1``,n) :` `            ``# If absolute values are``            ``# equal print pair.``            ``if` `(``abs``(arr[i]) ``=``=` `abs``(arr[j])) :``                ``v.append(``abs``(arr[i]))` `    ``# If size of vector is 0, therefore``    ``# there is no element with positive``    ``# negative value, print "0"``    ``if` `(``len``(v) ``=``=` `0``):``        ``return``;` `    ``# Sort the vector``    ``v.sort()` `    ``# Print the pair with negative``    ``# positive value.``    ``for` `i ``in` `range``(``len``( v)):``        ``print``(``-``v[i], "``" , v[i], end = "` `")` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ``arr ``=` `[ ``4``, ``8``, ``9``, ``-``4``, ``1``, ``-``1``, ``-``8``, ``-``9` `]``    ``n ``=` `len``(arr)``    ``printPairs(arr, n)` `# This code is contributed``# by ChitraNayal`

## C#

 `// C# program to find pairs of positive``// and negative values present in an array.``using` `System;``using` `System.Collections.Generic;` `class` `GFG``{` `    ``// Print pair with negative and positive value``    ``public` `static` `void` `printPairs(``int` `[]arr , ``int` `n)``    ``{``        ``List<``int``> v = ``new` `List<``int``>();``        ` `        ``// For each element of array.``        ``for` `(``int` `i = 0; i < n; i++)` `            ``// Try to find the negative value of``            ``// arr[i] from i + 1 to n``            ``for` `(``int` `j = i + 1; j < n; j++)` `                ``// If absolute values are equal``                ``// print pair.``                ``if` `(Math.Abs(arr[i]) ==``                                ``Math.Abs(arr[j]))``                    ``v.Add(Math.Abs(arr[i]));`  `        ``// If size of vector is 0, therefore there``        ``// is no element with positive negative``        ``// value, print "0"``        ``if` `(v.Count == 0)``            ``return``;    ``    ` `        ``// Sort the vector``        ``v.Sort();` `        ``// Print the pair with negative positive``        ``// value.``        ``for` `(``int` `i = 0; i < v.Count; i++)``            ``Console.Write(-v[i] + ``" "` `+``                                    ``v[i]);``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``int` `[]arr = { 4, 8, 9, -4, 1, -1, -8, -9 };``        ``int` `n = arr.Length;``        ``printPairs(arr, n);``    ``}``}` `// This code has been contributed by 29AjayKumar`

## Javascript

 ``
Output
`-1 1-4 4-8 8-9 9`

Method 2 (Hashing)
The idea is to use hashing. Traverse the given array, increase the count at absolute value of hash table. If count becomes 2, store its absolute value in another vector. And finally sort the vector. If the size of the vector is 0, print “0”, else for each term in vector print first its negative value and the positive value.

Below is the implementation of this approach:

## C++

 `// Efficient CPP program to find pairs of``// positive and negative values present in``// an array.``#include ``using` `namespace` `std;` `// Print pair with negative and positive value``void` `printPairs(``int` `arr[], ``int` `n)``{``    ``vector<``int``> v;``    ``unordered_map<``int``, ``bool``> cnt;` `    ``// For each element of array.``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// If element has not encounter early,``        ``// mark it on cnt array.``        ``if` `(cnt[``abs``(arr[i])] == 0)``            ``cnt[``abs``(arr[i])] = 1;` `        ``// If seen before, push it in vector (``        ``// given that elements are distinct)``        ``else` `{``            ``v.push_back(``abs``(arr[i]));``            ``cnt[``abs``(arr[i])] = 0;``        ``}``    ``}` `    ``if` `(v.size() == 0)``        ``return``;` `    ``sort(v.begin(), v.end());``    ``for` `(``int` `i = 0; i < v.size(); i++)``        ``cout << -v[i] << ``" "` `<< v[i] << ``" "``;``}` `// Driven Program``int` `main()``{``    ``int` `arr[] = { 4, 8, 9, -4, 1, -1, -8, -9 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``printPairs(arr, n);``    ``return` `0;``}`

## Java

 `// Efficient Java program to find pairs of``// positive and negative values present in``// an array.``import` `java.util.*;` `class` `GFG``{` `// Print pair with negative``// and positive value``static` `void` `printPairs(``int` `arr[], ``int` `n)``{``    ``ArrayList v = ``new` `ArrayList ();``    ``HashMap cnt = ``new` `HashMap();` `    ``// For each element of array.``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{` `        ``// If element has  encounter early,``        ``// then increment its count``        ``if` `(cnt.containsKey(Math.abs(arr[i])))``            ``cnt.put(Math.abs(arr[i]) , cnt.get(Math.abs(arr[i])) + ``1``);` `        ``// If element has not seen before,``          ``// then initialize its count to 1``        ``else``        ``{``             ` `            ``cnt.put(Math.abs(arr[i]), ``1``);``        ``}``        ``if``( cnt.get(Math.abs(arr[i])) == ``2` `){``          ``v.add(Math.abs(arr[i]));``        ``}``    ``}` `    ``if` `(v.size() == ``0``)``        ``return``;` `    ``Collections.sort(v);``    ``for` `(``int` `i = ``0``; i < v.size(); i++)``        ``System.out.print(``"-"` `+ v.get(i) +``                         ``" "` `+ v.get(i) + ``" "``);``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``4``, ``8``, ``9``, -``4``, ``1``, -``1``, -``8``, -``9` `};``    ``int` `n = arr.length;``    ``printPairs(arr, n);``}``}` `// This code is contributed by Prerna Saini`

## Python3

 `# Efficient Python3 program to find pairs of ``# positive and negative values present in``# an array. ` `# Print pair with negative and``# positive value``def` `printPairs(arr, n):``    ` `    ``s ``=` `set``()``    ``ret ``=` `[]``    ` `    ``# For each element of array.``    ``for` `i ``in` `arr:``        ``if` `abs``(i) ``in` `s:``            ``ret.append(``abs``(i))``        ``else``:``            ``s.add(``abs``(i))``            ` `    ``ret.sort()``    ` `    ``for` `i ``in` `range``(``0``, ``len``(ret)):``        ``print``(``-``ret[i], "``", ret[i], end = "` `")` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ` `    ``arr ``=` `[ ``4``, ``8``, ``9``, ``-``4``, ``1``, ``-``1``, ``-``8``, ``-``9` `]``    ``n ``=` `len``(arr)``    ` `    ``printPairs(arr, n)` `# This code is contributed by RohitOberoi`

## C#

 `// Efficient C# program to find pairs of``// positive and negative values present in``// an array.``using` `System;``using` `System.Collections.Generic;``class` `GFG``{``    ` `    ``// Print pair with negative and positive value``    ``static` `void` `printPairs(``int``[] arr, ``int` `n)``    ``{``        ``List<``int``> v = ``new` `List<``int``>();``        ``Dictionary<``int``, ``bool``> cnt = ``new` `Dictionary<``int``, ``bool``>();``     ` `        ``// For each element of array.``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``     ` `            ``// If element has not encounter early,``            ``// mark it on cnt array.``            ``if``(!cnt.ContainsKey(Math.Abs(arr[i])))``            ``{``                ``cnt[Math.Abs(arr[i])] = ``true``;``            ``}``            ``else` `if``(cnt[Math.Abs(arr[i])] == ``false``)``            ``{``                ``cnt[Math.Abs(arr[i])] = ``true``;``            ``}``            ``else``            ``{``                ``v.Add(Math.Abs(arr[i]));``                ``cnt[Math.Abs(arr[i])] = ``false``;``            ``}``        ``}``     ` `        ``if` `(v.Count == 0)``            ``return``;``     ` `        ``v.Sort();``        ``for` `(``int` `i = 0; i < v.Count; i++)``            ``Console.Write(-v[i] + ``" "` `+ v[i] + ``" "``);``    ``}` `  ``// Driver code``  ``static` `void` `Main()``  ``{``    ``int``[] arr = { 4, 8, 9, -4, 1, -1, -8, -9 };``    ``int` `n = arr.Length;``    ``printPairs(arr, n);``  ``}``}` `// This code is contributed by divyeshrabadiya07`
Output
`-1 1 -4 4 -8 8 -9 9 `

Method 3 (Using set) :

The idea is to use a set. Find the negative of the number in the set. If it exits then print both the numbers and if it does not exits then add it on to the set.

Below is the implementation of this approach:

## C++

 `// Efficient CPP program to find pairs of``// positive and negative values present in``// an array.``#include ``using` `namespace` `std;` `// Print pair with negative and positive value``void` `printPairs(``int` `arr[], ``int` `n)``{` `    ``unordered_set<``int``> hs ;``    ``vector<``int``> ans ;``    ``for``(``int` `i = 0 ; i < n ; i++ ){``        ``if``( hs.find((arr[i])*-1) != hs.end() ){``          ``if``(arr[i] < 0){``            ``cout << arr[i] << ``" "` `;``            ``cout << (arr[i]*-1) <<``" "` `;``          ``}``else``{``            ``cout << (arr[i]*-1) << ``" "` `;``            ``cout << arr[i] << ``" "` `;``          ``}``      ``}``      ``hs.insert(arr[i]) ;``  ``}``   ` `        ``return` `;``    ``}` `// Driven Program``int` `main()``{``    ``int` `arr[] = { 4, 8, 9, -4, 1, -1, -8, -9 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``printPairs(arr, n);``    ``return` `0;``}`
Output
`-4 4 -1 1 -8 8 -9 9 `

Time Complexity: O(n)

Auxiliary Space: O(n)

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