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

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 `

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 `

Output:

```-4, 4
-1, 1
-8, 8
-9, 9
```

Time Complexity: O(n)

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