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# Check if a given array is pairwise sorted or not

• Difficulty Level : Easy
• Last Updated : 30 Apr, 2021

An array is considered pairwise sorted if each successive pair of numbers is in sorted (non-decreasing) order. In case of odd elements, last element is ignored and result is based on remaining even number of elements.

Examples:

```Input : arr[] = {10, 15, 9, 9, 1, 5};
Output : Yes
Pairs are (10, 15), (9,  9) and (1, 5).
All these pairs are sorted in non-decreasing
order.

Input : arr[] = {10, 15, 8, 9, 10, 5};
Output : No
The last pair (10, 5) is not sorted.```

The idea is to traverse array from left to right. Compare elements pairwise, if any pair violates property, we return false. If no pair violates property, we return true.

## C++

 `// CPP program to check if an array is pair wise``// sorted.``#include ``using` `namespace` `std;` `// Check whether the array is pairwise sorted``// or not.``bool` `checkPairWiseSorted(``int` `arr[], ``int` `n)``{``    ``if` `(n == 0 || n == 1)``        ``return` `true``;``    ``for` `(``int` `i = 0; i < n; i += 2)``        ``if` `(arr[i] > arr[i + 1])``            ``return` `false``;``    ``return` `true``;``}` `// Driver program to test above function``int` `main()``{``   ``int` `arr[] = {2, 5, 3, 7, 9, 11};``   ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);  ``   ``if` `(checkPairWiseSorted(arr, n))``       ``printf``(``"Yes"``);``   ``else``       ``printf``(``"No"``);      ``   ``return` `0;``}`

## Java

 `// java program to check if an array``// is pair wise sorted.` `import` `java.io.*;` `public` `class` `GFG {``    ` `    ``// Check whether the array is``    ``// pairwise sorted or not.``    ``static` `boolean` `checkPairWiseSorted(``                          ``int` `[]arr, ``int` `n)``    ``{``        ``if` `(n == ``0` `|| n == ``1``)``            ``return` `true``;``            ` `        ``for` `(``int` `i = ``0``; i < n; i += ``2``)``            ``if` `(arr[i] > arr[i + ``1``])``                ``return` `false``;``                ` `        ``return` `true``;``    ``}``    ` `    ``// Driver program to test above``    ``// function``    ``static` `public` `void` `main (String[] args)``    ``{``        ``int` `[]arr = {``2``, ``5``, ``3``, ``7``, ``9``, ``11``};``        ``int` `n = arr.length;``        ` `        ``if` `(checkPairWiseSorted(arr, n))``            ``System.out.println(``"Yes"``);``        ``else``            ``System.out.println(``"No"``);``    ``}``}` `// This code is contributed by vt_m.`

## Python

 `# Python code to check whether the array``# is pairwise sorted or not.``def` `checkPairWiseSorted(a, n):``    ` `    ``if` `n ``=``=` `0` `or` `n ``=``=` `1``:``        ``return` `True``        ` `    ``for` `i ``in` `range``(``0``, n, ``2``):``        ``if` `a[i] > a[i ``+` `1``]:``            ``return` `False``    ` `    ``return` `True` `# Driver code``a ``=` `[``2``, ``5``, ``3``, ``7``, ``9``, ``11``]``n ``=` `len``(a)` `if` `checkPairWiseSorted(a, n):``    ``print` `"Yes"``else``:``    ``print` `"No"` `# This code is contributed by 'striver'.`

## C#

 `// C# program to check if an array is``// pair wise sorted.``using` `System;` `public` `class` `GFG {``    ` `    ``// Check whether the array is``    ``// pairwise sorted or not.``    ``static` `bool` `checkPairWiseSorted(``                      ``int` `[]arr, ``int` `n)``    ``{``        ``if` `(n == 0 || n == 1)``            ``return` `true``;``            ` `        ``for` `(``int` `i = 0; i < n; i += 2)``            ``if` `(arr[i] > arr[i + 1])``                ``return` `false``;``                ` `        ``return` `true``;``    ``}``    ` `    ``// Driver program to test above``    ``// function``    ``static` `public` `void` `Main ()``    ``{``        ``int` `[]arr = {2, 5, 3, 7, 9, 11};``        ``int` `n = arr.Length;``        ` `        ``if` `(checkPairWiseSorted(arr, n))``            ``Console.WriteLine(``"Yes"``);``        ``else``            ``Console.WriteLine(``"No"``);    ``    ``}``}` `// This code is contributed by vt_m.`

## PHP

 ` ``\$arr``[``\$i` `+ 1])``            ``return` `false;``    ``return` `true;``}` `// Driver program to test above function``\$arr` `= ``array``(2, 5, 3, 7, 9, 11);``\$n` `= ``count``(``\$arr``);` `if` `(checkPairWiseSorted(``\$arr``, ``\$n``))``    ``echo` `"Yes"``;``else``    ``echo` `"No"``;``    ` `// This code is contributed by anuj_67.``?>`

## Javascript

 ``

Output:

`Yes`

Time Complexity: O(n)
Space Complexity: O(1)

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