# Check if array can be converted into strictly decreasing sequence

Given an array arr[], the task is to check whether given array can be converted into a strictly decreasing sequence with the help of the below operation:

• Decrease any element(if it is greater than 1) by 1 in one operation

Examples:

Input: arr[] = {11, 11, 11, 11}
Output : Yes
Explanation:
The given sequence can be converted into
arr[] = {11, 10, 9, 8}

Input: arr[] = {1, 1}
Output: No
Explanation:
The given sequence cannot be converted into strictly decreasing sequence

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to check whether every element of the array is greater than or equal to (N – index of element), because if it is greater than or equal to (N – index of element) that means array can be converted into [N, N-1, N-2, ….1]

Below is the implementation of the above approach:

## C++

 `// C++ implementaion to check that ` `// array can be converted into a ` `// strictly decreasing sequence ` `#include ` `using` `namespace` `std; ` ` `  `// Function to check that array  ` `// can be converted into a ` `// strictly decreasing sequence ` `bool` `check(``int``* arr, ``int` `n) ` `{ ` `    ``bool` `flag = ``true``; ` ` `  `    ``// Loop to check that each element is ` `    ``// greater than the (N - index) ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``// If element is less than (N - index) ` `        ``if` `(arr[i] < n - i) { ` `            ``flag = ``false``; ` `        ``} ` `    ``} ` ` `  `    ``// If array can be converted ` `    ``if` `(flag) { ` `        ``return` `true``; ` `    ``} ` `    ``else` `{ ` `        ``return` `false``; ` `    ``} ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` `    ``int` `arr1[] = { 11, 11, 11, 11 }; ` `    ``int` `n1 = ``sizeof``(arr1) / ``sizeof``(arr1); ` ` `  `    ``// Function calling ` `    ``if` `(check(arr1, n1)) { ` `        ``cout << ``"Yes"` `<< endl; ` `    ``} ` `    ``else` `{ ` `        ``cout << ``"No"` `<< endl; ` `    ``} ` `} `

## Java

 `// Java implementaion to check that ` `// array can be converted into a ` `// strictly decreasing sequence ` `class` `GFG{ ` ` `  `// Function to check that array  ` `// can be converted into a ` `// strictly decreasing sequence ` `static` `boolean` `check(``int` `[]arr, ``int` `n) ` `{ ` `    ``boolean` `flag = ``true``; ` ` `  `    ``// Loop to check that each element is ` `    ``// greater than the (N - index) ` `    ``for` `(``int` `i = ``0``; i < n; i++) ` `    ``{ ` ` `  `        ``// If element is less than (N - index) ` `        ``if` `(arr[i] < n - i) ` `        ``{ ` `            ``flag = ``false``; ` `        ``} ` `    ``} ` ` `  `    ``// If array can be converted ` `    ``if` `(flag) ` `    ``{ ` `        ``return` `true``; ` `    ``} ` `    ``else`  `    ``{ ` `        ``return` `false``; ` `    ``} ` `} ` ` `  `// Driver Code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``int` `arr1[] = { ``11``, ``11``, ``11``, ``11` `}; ` `    ``int` `n1 = arr1.length; ` ` `  `    ``// Function calling ` `    ``if` `(check(arr1, n1)) ` `    ``{ ` `        ``System.out.print(``"Yes"` `+ ``"\n"``); ` `    ``} ` `    ``else`  `    ``{ ` `        ``System.out.print(``"No"` `+ ``"\n"``); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed by amal kumar choubey `

## Python3

 `# Python3 implementaion to check that ` `# array can be converted into a ` `# strictly decreasing sequence ` ` `  `# Function to check that array ` `# can be converted into a ` `# strictly decreasing sequence ` `def` `check(arr, n): ` ` `  `    ``flag ``=` `True``; ` ` `  `    ``# Loop to check that each element  ` `    ``# is greater than the (N - index) ` `    ``for` `i ``in` `range``(n): ` `         `  `        ``# If element is less than (N - index) ` `        ``if` `(arr[i] < n ``-` `i): ` `            ``flag ``=` `False``; ` `             `  `    ``# If array can be converted ` `    ``if` `(flag): ` `        ``return` `True``; ` `    ``else``: ` `        ``return` `False``; ` ` `  `# Driver Code ` `if` `__name__ ``=``=` `'__main__'``: ` `     `  `    ``arr1 ``=` `[ ``11``, ``11``, ``11``, ``11` `]; ` `    ``n1 ``=` `len``(arr1); ` ` `  `    ``# Function calling ` `    ``if` `(check(arr1, n1)): ` `        ``print``(``"Yes"``); ` `    ``else``: ` `        ``print``(``"No"``); ` ` `  `# This code is contributed by sapnasingh4991 `

## C#

 `// C# implementaion to check that ` `// array can be converted into a ` `// strictly decreasing sequence ` `using` `System; ` ` `  `class` `GFG{ ` ` `  `// Function to check that array  ` `// can be converted into a ` `// strictly decreasing sequence ` `static` `bool` `check(``int` `[]arr, ``int` `n) ` `{ ` `    ``bool` `flag = ``true``; ` ` `  `    ``// Loop to check that each element is ` `    ``// greater than the (N - index) ` `    ``for``(``int` `i = 0; i < n; i++) ` `    ``{ ` ` `  `       ``// If element is less than (N - index) ` `       ``if` `(arr[i] < n - i) ` `       ``{ ` `           ``flag = ``false``; ` `       ``} ` `    ``} ` ` `  `    ``// If array can be converted ` `    ``if` `(flag) ` `    ``{ ` `        ``return` `true``; ` `    ``} ` `    ``else` `    ``{ ` `        ``return` `false``; ` `    ``} ` `} ` ` `  `// Driver Code ` `static` `public` `void` `Main(String[] args) ` `{ ` `    ``int` `[]arr1 = { 11, 11, 11, 11 }; ` `    ``int` `n1 = arr1.Length; ` ` `  `    ``// Function calling ` `    ``if` `(check(arr1, n1)) ` `    ``{ ` `        ``Console.Write(``"Yes"` `+ ``"\n"``); ` `    ``} ` `    ``else` `    ``{ ` `        ``Console.Write(``"No"` `+ ``"\n"``); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```Yes
```

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