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Count of root to leaf paths whose permutation is palindrome in a Binary Tree
• Difficulty Level : Easy
• Last Updated : 16 Jun, 2021

Given a binary tree where node contains characters, the task is to count the number of paths from root vertex to leaf such that at least one permutation of the node values in the path is a palindrome.
Examples:

```Input:
2
/   \
3     1
/   \     \
3     4     2
/   \       /   \
2     1     2     1

Output: 2
Explanation:
Paths whose one of the
permutation are palindrome are -
2 => 3 => 3 => 2 and
2 => 1 => 2 => 1

Input:
2
/   \
a     3
/   \
2     a
Output: 2
Explanation:
Palindromic paths are
2 => a => 2 and
2 => a => a ```

Approach: The idea is to use pre-order traversal to traverse the binary tree and keep track of the path. Whenever a leaf node is reached then check that if any permutation of nodes values in the current path is a palindromic path or not.
To check the permutation of the values of the nodes is palindromic or not maintain the frequency of each character using a map. The path will be palindromic if the number of elements with odd frequency is at most 1.
Below is the implementation of the above approach:

## C++

 `// C++ implementation to count of``// the path whose permutation is``// a palindromic path` `#include ``using` `namespace` `std;``#define ll long long` `// Map to store the frequency``map<``char``, ``int``> freq;``int` `ans = 0;` `// Structure of the node``struct` `Node {``    ``char` `val;``    ``struct` `Node *left, *right;``};` `// Function to add new node``Node* newNode(``char` `key)``{``    ``Node* temp = ``new` `Node;``    ``temp->val = key;``    ``temp->left = temp->right = NULL;``    ``return` `(temp);``}` `// Function to check that the path``// is a palindrome or not``int` `checkPalin()``{``    ``int` `oddCount = 0;``    ``for` `(``auto` `x : freq) {``        ``if` `(x.second % 2 == 1)``            ``oddCount++;``    ``}``    ``return` `oddCount <= 1;``}` `// Function to count the root to``// leaf path whose permutation is``// a palindromic path``void` `cntpalin(Node* root)``{``    ``if` `(root == NULL)``        ``return``;``    ``freq[root->val]++;` `    ``if` `(root->left == NULL``        ``&& root->right == NULL) {` `        ``if` `(checkPalin() == ``true``)``            ``ans++;``    ``}``    ``cntpalin(root->left);``    ``cntpalin(root->right);``    ``freq[root->val]--;``}` `// Driver Code``int` `main()``{``    ``Node* root = newNode(``'2'``);``    ``root->left = newNode(``'a'``);``    ``root->left->right = newNode(``'a'``);``    ``root->left->left = newNode(``'2'``);``    ``root->left->right->right = newNode(``'2'``);``    ``root->right = newNode(``'3'``);` `    ``// Function Call``    ``cntpalin(root);` `    ``cout << ans << endl;``    ``return` `0;``}`

## Java

 `// Java implementation to count of``// the path whose permutation is``// a palindromic path``import` `java.util.*;``class` `GFG{` `// Map to store the frequency``static` `HashMap freq =``                        ``new` `HashMap<>();``static` `int` `ans = ``0``;` `// Structure of the node``static` `class` `Node``{``  ``char` `val;``  ``Node left, right;``};` `// Function to add new node``static` `Node newNode(``char` `key)``{``  ``Node temp = ``new` `Node();``  ``temp.val = key;``  ``temp.left = temp.right = ``null``;``  ``return` `(temp);``}` `// Function to check that the path``// is a palindrome or not``static` `boolean` `checkPalin()``{``  ``int` `oddCount = ``0``;``  ``for` `(Map.Entry x : freq.entrySet())``  ``{``    ``if` `(x.getValue() % ``2` `== ``1``)``      ``oddCount++;``  ``}` `  ``return` `oddCount <= ``1` `? ``true` `: ``false``;``}` `// Function to count the root to``// leaf path whose permutation is``// a palindromic path``static` `void` `cntpalin(Node root)``{``  ``if` `(root == ``null``)``    ``return``;``  ``if``(freq.containsKey(root.val))``  ``{``    ``freq.put(root.val,``    ``freq.get(root.val) + ``1``);``  ``}``  ``else``  ``{``    ``freq.put(root.val, ``1``);``  ``}` `  ``if` `(root.left == ``null` `&&``      ``root.right == ``null``)``  ``{``    ``if` `(checkPalin() == ``true``)``      ``ans++;``  ``}``  ` `  ``cntpalin(root.left);``  ``cntpalin(root.right);``  ` `  ``if``(freq.containsKey(root.val))``  ``{``    ``freq.put(root.val,``    ``freq.get(root.val) - ``1``);``  ``}``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``  ``Node root = newNode(``'2'``);``  ``root.left = newNode(``'a'``);``  ``root.left.right = newNode(``'a'``);``  ``root.left.left = newNode(``'2'``);``  ``root.left.right.right = newNode(``'2'``);``  ``root.right = newNode(``'3'``);` `  ``// Function Call``  ``cntpalin(root);` `  ``System.out.print(ans + ``"\n"``);``}``}` `// This code is contributed by Princi Singh`

## Python3

 `# Python3 program for the``# above approach``from` `collections ``import` `deque` `# A Tree node``class` `Node:``  ` `    ``def` `__init__(``self``, x):``      ` `        ``self``.data ``=` `x``        ``self``.left ``=` `None``        ``self``.right ``=` `None``        ` `freq ``=` `{}``ans ``=` `0` `# Function to check that the path``# is a palindrome or not``def` `checkPalin():``  ` `    ``oddCount ``=` `0``    ` `    ``for` `x ``in` `freq:``        ``if` `(freq[x] ``%` `2` `=``=` `1``):``            ``oddCount``+``=``1``    ``return` `oddCount <``=` `1` `# Function to count the root to``# leaf path whose permutation is``# a palindromic path``def` `cntpalin(root):``  ` `    ``global` `freq, ans``    ` `    ``if` `(root ``=``=` `None``):``        ``return``      ` `    ``freq[root.data] ``=` `freq.get(root.data,``                               ``0``) ``+` `1` `    ``if` `(root.left ``=``=` `None``        ``and` `root.right ``=``=` `None``):``        ``if` `(checkPalin() ``=``=` `True``):``            ``ans ``+``=` `1``            ` `    ``cntpalin(root.left)``    ``cntpalin(root.right)``    ``freq[root.data] ``-``=` `1` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``  ` `    ``root ``=` `Node(``'2'``)``    ``root.left ``=` `Node(``'a'``)``    ``root.left.right ``=` `Node(``'a'``)``    ``root.left.left ``=` `Node(``'2'``)``    ``root.left.right.right ``=` `Node(``'2'``)``    ``root.right ``=` `Node(``'3'``)` `    ``# Function Call``    ``cntpalin(root)` `    ``print``(ans)` `# This code is contributed by Rutvik_56`

## C#

 `// C# implementation to count of``// the path whose permutation is``// a palindromic path``using` `System;``using` `System.Collections.Generic;``class` `GFG{` `// Map to store the frequency``static` `Dictionary<``char``,``                  ``int``> freq = ``new` `Dictionary<``char``,``                                             ``int``>();``static` `int` `ans = 0;` `// Structure of the node``public` `class` `Node``{``  ``public` `char` `val;``  ``public` `Node left,``              ``right;``};` `// Function to add new node``static` `Node newNode(``char` `key)``{``  ``Node temp = ``new` `Node();``  ``temp.val = key;``  ``temp.left = temp.right = ``null``;``  ``return` `(temp);``}` `// Function to check that``// the path is a palindrome``// or not``static` `bool` `checkPalin()``{``  ``int` `oddCount = 0;``  ``foreach` `(KeyValuePair<``char``,``                        ``int``> x ``in` `freq)``  ``{``    ``if` `(x.Value % 2 == 1)``      ``oddCount++;``  ``}` `  ``return` `oddCount <= 1 ? ``true` `: ``false``;``}` `// Function to count the root to``// leaf path whose permutation is``// a palindromic path``static` `void` `cntpalin(Node root)``{``  ``if` `(root == ``null``)``    ``return``;``  ``if``(freq.ContainsKey(root.val))``  ``{``    ``freq[root.val] = freq[root.val] + 1;``  ``}``  ``else``  ``{``    ``freq.Add(root.val, 1);``  ``}` `  ``if` `(root.left == ``null` `&&``      ``root.right == ``null``)``  ``{``    ``if` `(checkPalin() == ``true``)``      ``ans++;``  ``}``  ` `  ``cntpalin(root.left);``  ``cntpalin(root.right);``  ` `  ``if``(freq.ContainsKey(root.val))``  ``{``    ``freq[root.val] = freq[root.val] - 1;``  ``}``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``  ``Node root = newNode(``'2'``);``  ``root.left = newNode(``'a'``);``  ``root.left.right = newNode(``'a'``);``  ``root.left.left = newNode(``'2'``);``  ``root.left.right.right = newNode(``'2'``);``  ``root.right = newNode(``'3'``);` `  ``// Function Call``  ``cntpalin(root);` `  ``Console.Write(ans + ``"\n"``);``}``}` `// This code is contributed by Amit Katiyar`

## Javascript

 ``
Output:
`2`

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