# Check if it is possible to redistribute the Array

Given an array arr[] of N integers, the task is to check if it is possible to redistribute the array such that for every 1 ≤ i ≤ N (1-based indexing) arr[i] = i. Redistributing the array means all the elements of the array can be chanaged to any other element but the sum of the resultant array must be equal to the original array sum.

Examples:

Input: arr[] = {7, 4, 1, 1, 2}
Output: Yes
7 + 4 + 1 + 1 + 2 = 15
1 + 2 + 3 + 4 + 5 = 15

Input: arr[] = {1, 1, 1, 1}
Output: No
1 + 1 + 1 + 1 = 4
1 + 2 + 3 + 4 = 10

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

Approach: It is given that the sum of the array must not change after the modification. So, calculate the sum of the given array and in order for the array to be of the form 1, 2, 3, …, N, the sum of the array elements must be (N * (N + 1)) / 2. Else, it is impossible.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function that returns true if the ` `// array can be redistributed to ` `// the form 1, 2, 3, ..., N ` `bool` `canRedistribute(``int``* a, ``int` `n) ` `{ ` ` `  `    ``// Calculate the sum of the array elements ` `    ``int` `sum = 0; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `        ``sum += a[i]; ` ` `  `    ``// If can be redistributed ` `    ``if` `(sum == (n * (n + 1)) / 2) ` `        ``return` `true``; ` ` `  `    ``return` `false``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `a[] = { 7, 4, 1, 1, 2 }; ` `    ``int` `n = ``sizeof``(a) / ``sizeof``(``int``); ` ` `  `    ``if` `(canRedistribute(a, n)) ` `        ``cout << ``"Yes"``; ` `    ``else` `        ``cout << ``"No"``; ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach ` `import` `java.io.*; ` ` `  `class` `GFG  ` `{ ` ` `  `// Function that returns true if the ` `// array can be redistributed to ` `// the form 1, 2, 3, ..., N ` `static` `boolean` `canRedistribute(``int` `[]a, ``int` `n) ` `{ ` ` `  `    ``// Calculate the sum of the array elements ` `    ``int` `sum = ``0``; ` `    ``for` `(``int` `i = ``0``; i < n; i++) ` `        ``sum += a[i]; ` ` `  `    ``// If can be redistributed ` `    ``if` `(sum == (n * (n + ``1``)) / ``2``) ` `        ``return` `true``; ` ` `  `    ``return` `false``; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main (String[] args)  ` `{ ` `    ``int` `a[] = { ``7``, ``4``, ``1``, ``1``, ``2` `}; ` `    ``int` `n = a.length; ` ` `  `    ``if` `(canRedistribute(a, n)) ` `        ``System.out.print( ``"Yes"``); ` `    ``else` `        ``System.out.print(``"No"``); ` `} ` `} ` ` `  `// This code is contributed by anuj_67.. `

## Python3

 `# Python implementation of the approach ` ` `  `# Function that returns true if the ` `# array can be redistributed to ` `# the form 1, 2, 3, ..., N ` `def` `canRedistribute(a, n): ` ` `  `    ``# Calculate the sum of the array elements ` `    ``sum` `=` `0``; ` `    ``for` `i ``in` `range``(n): ` `        ``sum` `+``=` `a[i]; ` ` `  `    ``# If can be redistributed ` `    ``if` `(``sum` `=``=` `(n ``*` `(n ``+` `1``)) ``/` `2``): ` `        ``return` `True``; ` ` `  `    ``return` `False``; ` ` `  `# Driver code ` ` `  `a ``=` `[``7``, ``4``, ``1``, ``1``, ``2` `]; ` `n ``=` `len``(a); ` ` `  `if` `(canRedistribute(a, n)): ` `    ``print``(``"Yes"``); ` `else``: ` `    ``print``(``"No"``); ` ` `  `# This code is contributed by 29AjayKumar `

## C#

 `// C# implementation of the approach ` `using` `System; ` `     `  `class` `GFG  ` `{ ` ` `  `// Function that returns true if the ` `// array can be redistributed to ` `// the form 1, 2, 3, ..., N ` `static` `Boolean canRedistribute(``int` `[]a, ``int` `n) ` `{ ` ` `  `    ``// Calculate the sum of the array elements ` `    ``int` `sum = 0; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `        ``sum += a[i]; ` ` `  `    ``// If can be redistributed ` `    ``if` `(sum == (n * (n + 1)) / 2) ` `        ``return` `true``; ` ` `  `    ``return` `false``; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main (String[] args)  ` `{ ` `    ``int` `[]a = { 7, 4, 1, 1, 2 }; ` `    ``int` `n = a.Length; ` ` `  `    ``if` `(canRedistribute(a, n)) ` `        ``Console.WriteLine( ``"Yes"``); ` `    ``else` `        ``Console.WriteLine(``"No"``); ` `} ` `} ` ` `  `/* This code is contributed by PrinciRaj1992 */`

Output:

```Yes
```

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