# Check if an array is increasing or decreasing

• Difficulty Level : Easy
• Last Updated : 31 Mar, 2022

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 satisfy 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 ``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 <= arr && 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 >= arr && 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 <= arr && 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);` `    ``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 <= arr &&``            ``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 >= arr &&``                 ``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 <= arr &&``                 ``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`

## Javascript

 ``

Output:

`Increasing`

Time Complexity: O(1)

Auxiliary Space: O(1)

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