# Check if a given array is pairwise sorted or not

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.
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 false.

## 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[0]);    ` `   ``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. ` `?> `

Output:

```Yes
```

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

This article is contributed by ASIPU PAWAN KUMAR. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Improved By : vt_m

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