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Check if an array is increasing or decreasing
  • Last Updated : 13 Sep, 2019

Given an array arr[] of N elements where N ≥ 2, the task is to check the type of array whether it is:

  1. Increasing.
  2. Decreasing.
  3. Increasing then decreasing.
  4. Decreasing then increasing.

Note that the given array is definitely one of the given types.

Examples:

Input: arr[] = {1, 2, 3, 4, 5}
Output: Increasing

Input: arr[] = {1, 2, 4, 3}
Output: Increasing then decreasing



Approach: The following conditions must satitisfy for:

  1. Increasing array: The first two and the last two elements must be in increasing order.
  2. Decreasing array: The first two and the last two elements must be in decreasing order.
  3. Increasing then decreasing array: The first two elements must be in increasing order and the last two elements must be in decreasing order.
  4. Decreasing then increasing array: The first two elements must be in decreasing order and the last two elements must be in increasing order.

Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to check the type of the array
void checkType(int arr[], int n)
{
  
    // If the first two and the last two elements
    // of the array are in increasing order
    if (arr[0] <= arr[1] && arr[n - 2] <= arr[n - 1])
        cout << "Increasing";
  
    // If the first two and the last two elements
    // of the array are in decreasing order
    else if (arr[0] >= arr[1] && arr[n - 2] >= arr[n - 1])
        cout << "Decreasing";
  
    // If the first two elements of the array are in
    // increasing order and the last two elements
    // of the array are in decreasing order
    else if (arr[0] <= arr[1] && arr[n - 2] >= arr[n - 1])
        cout << "Increasing then decreasing";
  
    // If the first two elements of the array are in
    // decreasing order and the last two elements
    // of the array are in increasing order
    else
        cout << "Decreasing then increasing";
}
  
// Driver code
int main()
{
    int arr[] = { 1, 2, 3, 4 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    checkType(arr, n);
  
    return 0;
}

Java




// Java implementation of the approach 
import java.math.*;
  
class GFG
{
  
    // Function to check the type of the array 
    public static void checkType(int arr[], int n) 
    
      
        // If the first two and the last two elements 
        // of the array are in increasing order 
        if (arr[0] <= arr[1] && 
            arr[n - 2] <= arr[n - 1]) 
            System.out.println("Increasing"); 
      
        // If the first two and the last two elements 
        // of the array are in decreasing order 
        else if (arr[0] >= arr[1] && 
                 arr[n - 2] >= arr[n - 1]) 
            System.out.println("Decreasing"); 
      
        // If the first two elements of the array are in 
        // increasing order and the last two elements 
        // of the array are in decreasing order 
        else if (arr[0] <= arr[1] &&
                 arr[n - 2] >= arr[n - 1]) 
            System.out.println("Increasing then decreasing"); 
  
        // If the first two elements of the array are in 
        // decreasing order and the last two elements 
        // of the array are in increasing order 
        else
            System.out.println("Decreasing then increasing");
    }
          
  
    // Driver code 
    public static void main(String[] args) 
    
        int[] arr = new int[]{ 1, 2, 3, 4 };
          
        int n = arr.length;
  
        checkType(arr, n); 
    }
}
  
// This code is contributed by Naman_Garg

Python3




# Python3 implementation of the approach 
  
# Function to check the type of the array 
def checkType(arr, n): 
  
    # If the first two and the last two elements 
    # of the array are in increasing order 
    if (arr[0] <= arr[1] and 
        arr[n - 2] <= arr[n - 1]) :
        print("Increasing"); 
  
    # If the first two and the last two elements 
    # of the array are in decreasing order 
    elif (arr[0] >= arr[1] and 
          arr[n - 2] >= arr[n - 1]) :
        print("Decreasing"); 
  
    # If the first two elements of the array are in 
    # increasing order and the last two elements 
    # of the array are in decreasing order 
    elif (arr[0] <= arr[1] and 
          arr[n - 2] >= arr[n - 1]) : 
        print("Increasing then decreasing"); 
  
    # If the first two elements of the array are in 
    # decreasing order and the last two elements 
    # of the array are in increasing order 
    else :
        print("Decreasing then increasing"); 
  
# Driver code 
if __name__ == "__main__"
  
    arr = [ 1, 2, 3, 4 ]; 
    n = len(arr); 
  
    checkType(arr, n); 
  
# This code is contributed by AnkitRai01

C#




// C# implementation of the approach 
using System;
class GFG
{
      
    // Function to check the type of the array 
    public static void checkType(int []arr, int n) 
    
      
        // If the first two and the last two elements 
        // of the array are in increasing order 
        if (arr[0] <= arr[1] && 
            arr[n - 2] <= arr[n - 1]) 
            Console.Write("Increasing"); 
      
        // If the first two and the last two elements 
        // of the array are in decreasing order 
        else if (arr[0] >= arr[1] && 
                 arr[n - 2] >= arr[n - 1]) 
            Console.Write("Decreasing"); 
      
        // If the first two elements of the array are in 
        // increasing order and the last two elements 
        // of the array are in decreasing order 
        else if (arr[0] <= arr[1] &&
                 arr[n - 2] >= arr[n - 1]) 
            Console.Write("Increasing then decreasing"); 
  
        // If the first two elements of the array are in 
        // decreasing order and the last two elements 
        // of the array are in increasing order 
        else
            Console.Write("Decreasing then increasing");
    }
  
    // Driver code 
    static public void Main ()
    {
        int[] arr = new int[]{ 1, 2, 3, 4 };
          
        int n = arr.Length;
  
        checkType(arr, n); 
    }
}
  
// This code is contributed by ajit
Output:
Increasing

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