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.


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. 
 

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// CPP program to check if an array is pair wise
// sorted.
#include <bits/stdc++.h>
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;
}
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// 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.
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# 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'.
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// 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.
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<?php
// PHP program to check if an array is
// pair wise sorted.
 
 
// Check whether the array is pairwise
// sorted or not.
function checkPairWiseSorted( $arr, $n)
{
    if ($n == 0 or $n == 1)
        return true;
    for ($i = 0; $i < $n; $i += 2)
        if ($arr[$i] > $arr[$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.
?>
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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, abhirup45

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