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Check if a given array is sorted in Spiral manner or not
  • Difficulty Level : Easy
  • Last Updated : 11 Jan, 2021

Given an array arr[] of size N, the task is to check if the array is spirally sorted or not. If found to be true, then print “YES”. Otherwise, print “NO”.

Note: An array is spirally sorted if arr[0] ≤ arr[N – 1] ≤ arr[1] ≤ arr[N – 2] …

Examples:

Input: arr[] = { 1, 10, 14, 20, 18, 12, 5 } 
Output: YES 
Explanation: 
arr[0] < arr[6]
arr[1] < arr[5]
arr[2] < arr[4]
Therefore, the required output is YES.

Input: arr[] = { 1, 2, 4, 3 } 
Output: NO



Approach: The idea is to traverse the array and for every array element, say arr[i], check if arr[i] is less than or equal to arr[N – i – 1] and arr[N – i – 1] less than or equal to arr[i + 1] or not. If found to be false, then print “NO”. Otherwise, if all array elements satisfy the condition, then print “YES”. Follow the steps below to solve the problem:

  • Initialize two variables, say start and end, to store the start and end indices of the given array.
  • Iterate a loop while start is less than end, and check if arr[start] less than or equal to arr[end] and arr[end] is less than or equal to arr[start + 1] or not. If found to be false, then print “NO”.
  • Otherwise, print “YES”.

Below is the implementation of the above approach:

C++14

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// C++ program to implement
// the above approach
#include <iostream>
using namespace std;
 
// Function to check if the array is
// spirally sorted or not
bool isSpiralSorted(int arr[], int n)
{
 
    // Stores start index
    // of the array
    int start = 0;
 
    // Stores end index
    // of an array
    int end = n - 1;
 
    while (start < end) {
 
        // If arr[start]
        // greater than arr[end]
        if (arr[start] > arr[end]) {
            return false;
        }
 
        // Update start
        start++;
 
        // If arr[end]
        // greater than arr[start]
        if (arr[end] > arr[start]) {
            return false;
        }
 
        // Update end
        end--;
    }
 
    return true;
}
 
// Driver Code
int main()
{
    int arr[] = { 1, 10, 14, 20, 18, 12, 5 };
 
    int N = sizeof(arr) / sizeof(arr[0]);
 
    // Function Call
    if (isSpiralSorted(arr, N))
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
    return 0;
}

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Java

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// Java program to implement
// the above approach
import java.util.*;
 
class GFG{
 
  // Function to check if the array is
  // spirally sorted or not
  static boolean isSpiralSorted(int[] arr, int n)
  {
 
    // Stores start index
    // of the array
    int start = 0;
 
    // Stores end index
    // of an array
    int end = n - 1;
 
    while (start < end)
    {
 
      // If arr[start]
      // greater than arr[end]
      if (arr[start] > arr[end])
      {
        return false;
      }
 
      // Update start
      start++;
 
      // If arr[end]
      // greater than arr[start]
      if (arr[end] > arr[start])
      {
        return false;
      }
 
      // Update end
      end--;
    }       
    return true;
  }
 
  // Driver code
  public static void main(String[] args)
  {
    int[] arr = { 1, 10, 14, 20, 18, 12, 5 };  
    int N = arr.length;
 
    // Function Call
    if (isSpiralSorted(arr, N) != false)
      System.out.print("YES");
    else
      System.out.print("NO");
  }
}
 
// This code is contributed by sanjoy_62

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Python3

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# Python3 program to implement
# the above approach
 
# Function to check if the array is
# spirally sorted or not
def isSpiralSorted(arr, n) :
 
    # Stores start index
    # of the array
    start = 0;
 
    # Stores end index
    # of an array
    end = n - 1;
    while (start < end) :
 
        # If arr[start]
        # greater than arr[end]
        if (arr[start] > arr[end]) :
            return False;
 
        # Update start
        start += 1;
 
        # If arr[end]
        # greater than arr[start]
        if (arr[end] > arr[start]) :
            return False;
 
        # Update end
        end -= 1;
    return True;
 
# Driver Code
if __name__ ==  "__main__" :
    arr = [ 1, 10, 14, 20, 18, 12, 5 ];
    N = len(arr);
 
    # Function Call
    if (isSpiralSorted(arr, N)) :
        print("YES");
    else :
        print("NO");
         
    # This code is contributed by AnkThon

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C#

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// C# program to implement
// the above approach
using System;
using System.Collections.Generic;
class GFG
{
     
    // Function to check if the array is
    // spirally sorted or not
    static bool isSpiralSorted(int[] arr, int n)
    {
       
        // Stores start index
        // of the array
        int start = 0;
       
        // Stores end index
        // of an array
        int end = n - 1;
       
        while (start < end)
        {
       
            // If arr[start]
            // greater than arr[end]
            if (arr[start] > arr[end])
            {
                return false;
            }
       
            // Update start
            start++;
       
            // If arr[end]
            // greater than arr[start]
            if (arr[end] > arr[start])
            {
                return false;
            }
       
            // Update end
            end--;
        }
       
        return true;
    }
 
  // Driver code
  static void Main()
  {
    int[] arr = { 1, 10, 14, 20, 18, 12, 5 };  
    int N = arr.Length;
   
    // Function Call
    if (isSpiralSorted(arr, N))
        Console.WriteLine("YES");
    else
        Console.WriteLine("NO");
  }
}
 
// This code is contributed bydivyesh072019

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Output: 

YES

 

Time Complexity: O(N) 
Auxiliary Space: O(1)

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