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Check if the given Prufer sequence is valid or not
• Difficulty Level : Expert
• Last Updated : 07 May, 2021

Given a Prufer sequence of N integers, the task is to check if the given sequence is a valid Prufer sequence or not.
Examples:

```Input: arr[] = {4, 1, 3, 4}
Output: Valid
The tree is:
2----4----3----1----5
|
6

Input: arr[] = {4, 1, 7, 4}
Output: Invalid ```

Approach: Since we know the Prufer sequence is of length N – 2 where N is the number of vertices. Hence we need to check if the Prufer sequence consists of elements which are in the range [1, N].
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function that returns true if``// given Prufer sequence is valid``bool` `isValidSeq(``int` `a[], ``int` `n)``{``    ``int` `nodes = n + 2;` `    ``// Iterate in the Prufer sequence``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// If out of range``        ``if` `(a[i] < 1 || a[i] > nodes)``            ``return` `false``;``    ``}` `    ``return` `true``;``}` `// Driver code``int` `main()``{``    ``int` `a[] = { 4, 1, 3, 4 };``    ``int` `n = ``sizeof``(a) / ``sizeof``(a);``    ``if` `(isValidSeq(a, n))``        ``cout << ``"Valid"``;``    ``else``        ``cout << ``"Invalid"``;` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``import` `java.io.*;` `class` `GFG``{`  `// Function that returns true if``// given Prufer sequence is valid``static` `boolean` `isValidSeq(``int` `[]a, ``int` `n)``{``    ``int` `nodes = n + ``2``;` `    ``// Iterate in the Prufer sequence``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{` `        ``// If out of range``        ``if` `(a[i] < ``1` `|| a[i] > nodes)``            ``return` `false``;``    ``}` `    ``return` `true``;``}` `// Driver code``public` `static` `void` `main (String[] args)``{``    ``int` `a[] = { ``4``, ``1``, ``3``, ``4` `};``    ``int` `n = a.length;``    ``if` `(isValidSeq(a, n))``        ``System.out.println( ``"Valid"``);``    ``else``        ``System.out.print( ``"Invalid"``);``}``}` `// This code is contributed by anuj_67..`

## Python3

 `# Python3 implementation of the approach` `# Function that returns true if``# given Prufer sequence is valid``def` `isValidSeq(a, n) :` `    ``nodes ``=` `n ``+` `2``;` `    ``# Iterate in the Prufer sequence``    ``for` `i ``in` `range``(n) :` `        ``# If out of range``        ``if` `(a[i] < ``1` `or` `a[i] > nodes) :``            ``return` `False``;``    ` `    ``return` `True``;` `# Driver code``if` `__name__ ``=``=` `"__main__"` `:` `    ``a ``=` `[ ``4``, ``1``, ``3``, ``4` `];``    ` `    ``n ``=` `len``(a);``    ` `    ``if` `(isValidSeq(a, n)) :``        ``print``(``"Valid"``);``    ``else` `:``        ``print``(``"Invalid"``);``        ` `# This code is contributed by AnkitRai01`

## C#

 `// C# implementation of the approach``using` `System;``    ` `class` `GFG``{`  `// Function that returns true if``// given Prufer sequence is valid``static` `Boolean isValidSeq(``int` `[]a, ``int` `n)``{``    ``int` `nodes = n + 2;` `    ``// Iterate in the Prufer sequence``    ``for` `(``int` `i = 0; i < n; i++)``    ``{` `        ``// If out of range``        ``if` `(a[i] < 1 || a[i] > nodes)``            ``return` `false``;``    ``}` `    ``return` `true``;``}` `// Driver code``public` `static` `void` `Main (String[] args)``{``    ``int` `[]a = { 4, 1, 3, 4 };``    ``int` `n = a.Length;``    ``if` `(isValidSeq(a, n))``        ``Console.WriteLine( ``"Valid"``);``    ``else``    ``Console.WriteLine( ``"Invalid"``);``}``}` `// This code has been contributed by 29AjayKumar`

## Javascript

 ``
Output:
`Valid`

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