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Print all the pairs that contains the positive and negative values of an element

• Last Updated : 09 Jul, 2021

Given an array of distinct integers, print all the pairs having a positive value and negative value of a number that exists in the array.
Note: Order of the pairs doesn’t matter.
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```

A naive approach is to run two loops i.e. Consider each element of the array using the outer loop and search for its corresponding positive/negative value in the array using an inner loop. Similarly, find all the pairs. Time Complexity of this approach will be O( n2).
A better approach is to use sorting i.e. first sort the array and then for each negative element, do a binary search to find its counterpart (+ve number). If found, print that pair. If the current element is positive then break that loop as after that there will be all the positive numbers.

C++

 `// CPP program to find pairs of positive``// and negative values present in an array.``#include ``using` `namespace` `std;` `void` `printPairs(``int` `arr[], ``int` `n)``{``    ``bool` `pair_exists = ``false``;``    ``// Sort the array``    ``sort(arr, arr + n);` `    ``// Traverse the array``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// For every arr[i] < 0 element,``        ``// do a binary search for arr[i] > 0.``        ``if` `(arr[i] < 0) {` `            ``// If found, print the pair.``            ``if` `(binary_search(arr, arr + n, -arr[i])) {``                ``cout << arr[i] << ``", "` `<< -arr[i] << endl;` `                ``pair_exists = ``true``;``            ``}``        ``}` `        ``else``            ``break``;``    ``}` `    ``if` `(pair_exists == ``false``)``        ``cout << ``"No such pair exists"``;``}` `// Driver code``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.*;``class` `GFG``{``static` `void` `printPairs(``int` `arr[], ``int` `n)``{``    ``boolean` `pair_exists = ``false``;``    ` `    ``// Sort the array``    ``Arrays.sort(arr);` `    ``// Traverse the array``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{` `        ``// For every arr[i] < 0 element,``        ``// do a binary search for arr[i] > 0.``        ``if` `(arr[i] < ``0``)``        ``{` `            ``// If found, print the pair.``            ``if` `(java.util.Arrays.binarySearch(arr, -arr[i])!=-``1``)``            ``{``                ``System.out.println(arr[i] + ``", "` `+ -arr[i] );` `                ``pair_exists = ``true``;``            ``}``        ``}` `        ``else``            ``break``;``    ``}` `    ``if` `(pair_exists == ``false``)``        ``System.out.println(``"No such pair exists"``);``}` `// 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 Arnab Kundu`

Python 3

 `# Python3 program to find pairs of positive``# and negative values present in an array.` `# function for binary search``def` `binary_search(a, x, lo``=``0``, hi``=``None``):``    ``if` `hi ``is` `None``:``        ``hi ``=` `len``(a)``    ``while` `lo < hi:``        ``mid ``=` `(lo``+``hi)``/``/``2``        ``midval ``=` `a[mid]``        ``if` `midval < x:``            ``lo ``=` `mid``+``1``        ``elif` `midval > x:``            ``hi ``=` `mid``        ``else``:``            ``return` `mid``    ``return` `-``1` `def` `printPairs(arr, n):` `    ``pair_exists ``=` `False``    ``# Sort the array``    ``arr.sort()` `    ``# Traverse the array``    ``for` `i ``in` `range``(n):``    `  `        ``# For every arr[i] < 0 element,``        ``# do a binary search for arr[i] > 0.``        ``if` `(arr[i] < ``0``):` `            ``# If found, print the pair.``            ``if` `(binary_search(arr,``-``arr[i])):``                ``print``(arr[i] , ``", "` `, ``-``arr[i])` `                ``pair_exists ``=` `True``        ` `        `  `        ``else``:``            ``break``    `  `    ``if` `(pair_exists ``=``=` `False``):``        ``print``(``"No such pair exists"``)`  `# 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 ash264`

C#

 `// C# program to find pairs``// of positive and negative``// values present in an array.` `using` `System;``public` `class` `GFG{` `static` `void` `printPairs(``int` `[]arr, ``int` `n)``{``    ``bool` `pair_exists = ``false``;``    ` `    ``// Sort the array``    ``Array.Sort(arr);` `    ``// Traverse the array``    ``for` `(``int` `i = 0; i < n; i++)``    ``{` `        ``// For every arr[i] < 0 element,``        ``// do a binary search for arr[i] > 0.``        ``if` `(arr[i] < 0)``        ``{` `            ``// If found, print the pair.``            ``if` `(Array.BinarySearch(arr, -arr[i])!=-1)``            ``{``                ``Console.WriteLine(arr[i] + ``", "` `+ -arr[i] );` `                ``pair_exists = ``true``;``            ``}``        ``}` `        ``else``            ``break``;``    ``}` `    ``if` `(pair_exists == ``false``)``        ``Console.WriteLine(``"No such pair exists"``);``}` `// Driver code``public` `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 29AjayKumar`

Javascript

 ``
Output:
```-9, 9
-8, 8
-4, 4
-1, 1```

Time Complexity: O(nlogn)
An efficient Approach is to use hashing. Below are the required steps:

• Start traversing the array.
• Store all the psoitve values in an unordered_set.
• Check for each negative element, if their corresponding positive element exists in the set or not.
• If yes, print the pair
• Also, maintain a flag to check if no such pair exists.

C++

 `// CPP program to find pairs of positive``// and negative values present in an array``#include ``using` `namespace` `std;` `// Function to print pairs of positive``// and negative values present in the array``void` `printPairs(``int` `arr[], ``int` `n)``{``    ``unordered_set<``int``> pairs;``    ``bool` `pair_exists = ``false``;` `    ``// Store all the positive elements``    ``// in the unordered_set``    ``for` `(``int` `i = 0; i < n; i++)``        ``if` `(arr[i] > 0)``            ``pairs.insert(arr[i]);` `    ``// Start traversing the array``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// Check if the positive value of current``        ``// element exists in the set or not``        ``if` `(arr[i] < 0)``            ``if` `(pairs.find(-arr[i]) != pairs.end())` `            ``{ ``// Print that pair``                ``cout << arr[i] << ``", "` `<< -arr[i] << endl;` `                ``pair_exists = ``true``;``            ``}``    ``}` `    ``if` `(pair_exists == ``false``)``        ``cout << ``"No such pair exists"``;``}` `// Driver code``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.*;``class` `GFG``{` `// Function to print pairs of positive``// and negative values present in the array``static` `void` `printPairs(``int` `arr[], ``int` `n)``{``    ``Set pairs = ``new` `HashSet();``    ``boolean` `pair_exists = ``false``;` `    ``// Store all the positive elements``    ``// in the unordered_set``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``if` `(arr[i] > ``0``)``            ``pairs.add(arr[i]);` `    ``// Start traversing the array``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{` `        ``// Check if the positive value of current``        ``// element exists in the set or not``        ``if` `(arr[i] < ``0``)``            ``if` `(pairs.contains(-arr[i]))``            ``{``                ``// Print that pair``                ``System.out.println(arr[i] + ``", "` `+ -arr[i]);` `                ``pair_exists = ``true``;``            ``}``    ``}` `    ``if` `(pair_exists == ``false``)``        ``System.out.println(``"No such pair exists"``);``}` `// 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 Arnab Kundu`

Python3

 `# Python3 program to find pairs of positive``# and negative values present in an array` `# Function to print pairs of positive``# and negative values present in the array``def` `printPairs(arr, n):` `    ``pairs ``=` `set``()``    ``pair_exists ``=` `False` `    ``# Store all the positive elements``    ``# in the unordered_set``    ``for` `i ``in` `range``(``0``, n):``        ``if` `arr[i] > ``0``:``            ``pairs.add(arr[i])` `    ``# Start traversing the array``    ``for` `i ``in` `range``(``0``, n):` `        ``# Check if the positive value of current``        ``# element exists in the set or not``        ``if` `arr[i] < ``0``:``            ``if` `(``-``arr[i]) ``in` `pairs:` `            ``# Print that pair``                ``print``(``"{}, {}"``.``format``(arr[i], ``-``arr[i]))``                ``pair_exists ``=` `True` `    ``if` `pair_exists ``=``=` `False``:``        ``print``(``"No such pair exists"``)` `# 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 Rituraj Jain`

C#

 `// C# program to find pairs of positive``// and negative values present in an array``using` `System;``using` `System.Collections.Generic;` `class` `GFG``{` `// Function to print pairs of positive``// and negative values present in the array``static` `void` `printPairs(``int` `[]arr, ``int` `n)``{``    ``HashSet<``int``> pairs = ``new` `HashSet<``int``>();``    ``bool` `pair_exists = ``false``;` `    ``// Store all the positive elements``    ``// in the unordered_set``    ``for` `(``int` `i = 0; i < n; i++)``        ``if` `(arr[i] > 0)``            ``pairs.Add(arr[i]);` `    ``// Start traversing the array``    ``for` `(``int` `i = 0; i < n; i++)``    ``{` `        ``// Check if the positive value of current``        ``// element exists in the set or not``        ``if` `(arr[i] < 0)``            ``if` `(pairs.Contains(-arr[i]))``            ``{``                ``// Print that pair``                ``Console.WriteLine(arr[i] + ``", "` `+ -arr[i]);` `                ``pair_exists = ``true``;``            ``}``    ``}` `    ``if` `(pair_exists == ``false``)``        ``Console.WriteLine(``"No such pair exists"``);``}` `// 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 PrinciRaj1992`

Javascript

 ``
Output:
```-4, 4
-1, 1
-8, 8
-9, 9```

Time Complexity: O(n)

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