# Program to check if an array is sorted or not (Iterative and Recursive)

Given an array of size n, write a program to check if it is sorted in ascending order or not. Equal values are allowed in array and two consecutive equal values are considered sorted.

Examples:

```Input : 20 21 45 89 89 90
Output : Yes

Input : 20 20 45 89 89 90
Output : Yes

Input : 20 20 78 98 99 97
Output : No
```

## Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Recursive approach:

The basic idea for recursive approach:

```1: If size of array is zero or one, return true.
2: Check last two elements of array, if they are
sorted, perform a recursive call with n-1
else, return false.
If all the elements will be found sorted, n will
eventually fall to one, satisfying Step 1.
```

Below is the implementation using recursion:

## C++

 `// Recursive approach to check if an ` `// Array is sorted or not ` `#include ` `using` `namespace` `std; ` ` `  `// Function that returns 0 if a pair ` `// is found unsorted ` `int` `arraySortedOrNot(``int` `arr[], ``int` `n) ` `{ ` `    ``// Array has one or no element or the ` `    ``// rest are already checked and approved. ` `    ``if` `(n == 1 || n == 0) ` `        ``return` `1; ` ` `  `    ``// Unsorted pair found (Equal values allowed) ` `    ``if` `(arr[n - 1] < arr[n - 2]) ` `        ``return` `0; ` ` `  `    ``// Last pair was sorted ` `    ``// Keep on checking ` `    ``return` `arraySortedOrNot(arr, n - 1); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 20, 23, 23, 45, 78, 88 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` `    ``if` `(arraySortedOrNot(arr, n)) ` `        ``cout << ``"Yes\n"``; ` `    ``else` `        ``cout << ``"No\n"``; ` `} `

## Java

 `// Recursive approach to check if an ` `// Array is sorted or not ` ` `  `class` `CkeckSorted { ` `    ``// Function that returns 0 if a pair ` `    ``// is found unsorted ` `    ``static` `int` `arraySortedOrNot(``int` `arr[], ``int` `n) ` `    ``{ ` `        ``// Array has one or no element or the ` `        ``// rest are already checked and approved. ` `        ``if` `(n == ``1` `|| n == ``0``) ` `            ``return` `1``; ` ` `  `        ``// Unsorted pair found (Equal values allowed) ` `        ``if` `(arr[n - ``1``] < arr[n - ``2``]) ` `            ``return` `0``; ` ` `  `        ``// Last pair was sorted ` `        ``// Keep on checking ` `        ``return` `arraySortedOrNot(arr, n - ``1``); ` `    ``} ` ` `  `    ``// main function ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `arr[] = { ``20``, ``23``, ``23``, ``45``, ``78``, ``88` `}; ` `        ``int` `n = arr.length; ` `        ``if` `(arraySortedOrNot(arr, n) != ``0``) ` `            ``System.out.println(``"Yes"``); ` `        ``else` `            ``System.out.println(``"No"``); ` `    ``} ` `} `

## Python3

 `# Recursive approach to check if an ` `# Array is sorted or not ` ` `  `# Function that returns 0 if a pair ` `# is found unsorted ` `def` `arraySortedOrNot(arr): ` `     `  `    ``# Calculating length ` `    ``n ``=` `len``(arr) ` `     `  `    ``# Array has one or no element or the ` `    ``# rest are already checked and approved. ` `    ``if` `n ``=``=` `1` `or` `n ``=``=` `0``: ` `        ``return` `True` `         `  `    ``# Recursion applied till last element ` `    ``return` `arr[``0``]<``=` `arr[``1``] ``and` `arraySortedOrNot(arr[``1``:]) ` ` `  ` `  `arr ``=` `[``20``, ``23``, ``23``, ``45``, ``78``, ``88``] ` ` `  `# Displaying result ` `if` `arraySortedOrNot(arr): ``print``(``"Yes"``) ` `else``: ``print``(``"No"``)  `

## C#

 `// Recursive approach to check if an ` `// Array is sorted or not ` `using` `System; ` `     `  `class` `CkeckSorted ` `{ ` `    ``// Function that returns 0 if a pair ` `    ``// is found unsorted ` `    ``static` `int` `arraySortedOrNot(``int` `[]arr, ``int` `n) ` `    ``{ ` `        ``// Array has one or no element or the ` `        ``// rest are already checked and approved. ` `        ``if` `(n == 1 || n == 0) ` `            ``return` `1; ` ` `  `        ``// Unsorted pair found (Equal values allowed) ` `        ``if` `(arr[n - 1] < arr[n - 2]) ` `            ``return` `0; ` ` `  `        ``// Last pair was sorted ` `        ``// Keep on checking ` `        ``return` `arraySortedOrNot(arr, n - 1); ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `Main(String[] args) ` `    ``{ ` `        ``int` `[]arr = { 20, 23, 23, 45, 78, 88 }; ` `        ``int` `n = arr.Length; ` `        ``if` `(arraySortedOrNot(arr, n) != 0) ` `            ``Console.WriteLine(``"Yes"``); ` `        ``else` `            ``Console.WriteLine(``"No"``); ` `    ``} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```Yes
```

Time Complexity: O(n)
Auxiliary Space: O(n) for Recursion Call Stack.

Iterative approach: The idea is pretty much the same. The benefit of the iterative approach is it avoids the usage of recursion stack space and recursion overhead.

Below is the implementation using iteration:

## C++

 `// C++ program to check if an ` `// Array is sorted or not ` `#include ` `using` `namespace` `std; ` ` `  `// Function that returns true if array is ` `// sorted in non-decreasing order. ` `bool` `arraySortedOrNot(``int` `arr[], ``int` `n) ` `{ ` `    ``// Array has one or no element ` `    ``if` `(n == 0 || n == 1) ` `        ``return` `true``; ` ` `  `    ``for` `(``int` `i = 1; i < n; i++) ` ` `  `        ``// Unsorted pair found ` `        ``if` `(arr[i - 1] > arr[i]) ` `            ``return` `false``; ` ` `  `    ``// No unsorted pair found ` `    ``return` `true``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 20, 23, 23, 45, 78, 88 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` `    ``if` `(arraySortedOrNot(arr, n)) ` `        ``cout << ``"Yes\n"``; ` `    ``else` `        ``cout << ``"No\n"``; ` `} `

## Java

 `// Recursive approach to check if an ` `// Array is sorted or not ` `class` `GFG { ` ` `  `    ``// Function that returns true if array is ` `    ``// sorted in non-decreasing order. ` `    ``static` `boolean` `arraySortedOrNot(``int` `arr[], ``int` `n) ` `    ``{ ` ` `  `        ``// Array has one or no element ` `        ``if` `(n == ``0` `|| n == ``1``) ` `            ``return` `true``; ` ` `  `        ``for` `(``int` `i = ``1``; i < n; i++) ` ` `  `            ``// Unsorted pair found ` `            ``if` `(arr[i - ``1``] > arr[i]) ` `                ``return` `false``; ` ` `  `        ``// No unsorted pair found ` `        ``return` `true``; ` `    ``} ` ` `  `    ``// driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` ` `  `        ``int` `arr[] = { ``20``, ``23``, ``23``, ``45``, ``78``, ``88` `}; ` `        ``int` `n = arr.length; ` ` `  `        ``if` `(arraySortedOrNot(arr, n)) ` `            ``System.out.print(``"Yes\n"``); ` `        ``else` `            ``System.out.print(``"No\n"``); ` `    ``} ` `} ` ` `  `// This code is contributed by Anant Agarwal. `

## Python3

 `# Python3 program to check if an ` `# Array is sorted or not ` ` `  `# Function that returns true if array is ` `# sorted in non-decreasing order. ` `def` `arraySortedOrNot(arr, n): ` ` `  `    ``# Array has one or no element ` `    ``if` `(n ``=``=` `0` `or` `n ``=``=` `1``): ` `        ``return` `True` ` `  `    ``for` `i ``in` `range``(``1``, n): ` ` `  `        ``# Unsorted pair found ` `        ``if` `(arr[i``-``1``] > arr[i]): ` `            ``return` `False` ` `  `    ``# No unsorted pair found ` `    ``return` `True` ` `  ` `  `# Driver code ` `arr ``=` `[``20``, ``23``, ``23``, ``45``, ``78``, ``88``] ` `n ``=` `len``(arr) ` `if` `(arraySortedOrNot(arr, n)): ` `    ``print``(``"Yes"``) ` `else``: ` `    ``print``(``"No"``) ` `     `  `# This code is contributed by Anant Agarwal. `

## C#

 `// Recursive approach to check if an ` `// Array is sorted or not ` `using` `System; ` ` `  `class` `GFG ` `{ ` ` `  `    ``// Function that returns true if array is ` `    ``// sorted in non-decreasing order. ` `    ``static` `bool` `arraySortedOrNot(``int` `[]arr, ``int` `n) ` `    ``{ ` ` `  `        ``// Array has one or no element ` `        ``if` `(n == 0 || n == 1) ` `            ``return` `true``; ` ` `  `        ``for` `(``int` `i = 1; i < n; i++) ` ` `  `            ``// Unsorted pair found ` `            ``if` `(arr[i - 1] > arr[i]) ` `                ``return` `false``; ` ` `  `        ``// No unsorted pair found ` `        ``return` `true``; ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main(String[] args) ` `    ``{ ` `        ``int` `[]arr = { 20, 23, 23, 45, 78, 88 }; ` `        ``int` `n = arr.Length; ` ` `  `        ``if` `(arraySortedOrNot(arr, n)) ` `            ``Console.Write(``"Yes\n"``); ` `        ``else` `            ``Console.Write(``"No\n"``); ` `    ``} ` `} ` ` `  `// This code is contributed by PrinciRaj1992 `

Output:

`Yes`

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

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Improved By : princiraj1992, 29AjayKumar

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