# Convert Ternary Expression to a Binary Tree

Given a string that contains ternary expressions. The expressions may be nested, task is convert the given ternary expression to a binary Tree.

Examples:

```Input :  string expression =   a?b:c
Output :        a
/  \
b    c

Input : expression =  a?b?c:d:e
Output :     a
/  \
b    e
/  \
c    d
```

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

Idea is that we traverse a string make first character as root and do following step recursively .
1. If we see Symbol ‘?’
…….. then we add next character as the left child of root.
2. If we see Symbol ‘:’
…….. then we add it as the right child of current root.
do this process until we traverse all element of “String”.

Below is the implementation of above idea

## C++

 `// C++ program to convert a ternary expression to ` `// a tree. ` `#include ` `using` `namespace` `std; ` ` `  `// tree structure ` `struct` `Node ` `{ ` `    ``char` `data; ` `    ``Node *left, *right; ` `}; ` ` `  `// function create a new node ` `Node *newNode(``char` `Data) ` `{ ` `    ``Node *new_node = ``new` `Node; ` `    ``new_node->data = Data; ` `    ``new_node->left = new_node->right = NULL; ` `    ``return` `new_node; ` `} ` ` `  `// Function to convert Ternary Expression to a Binary ` `// Tree. It return the root of tree ` `//Notice that we pass index i by reference because we want to skip the characters in the subtree ` `Node *convertExpression(string str, ``int` `& i) ` `{ ` `    ``// store current character of expression_string  ` `    ``// [ 'a' to 'z']  ` `    ``Node * root =newNode(str[i]); ` ` `  `    ``//If it was last character return ` `    ``//Base Case ` `    ``if``(i==str.length()-1) ``return` `root; ` ` `  `    ``// Move ahead in str  ` `    ``i++; ` `    ``//If the next character is '?'.Then there will be subtree for the current node ` `    ``if``(str[i]==``'?'``) ` `    ``{ ` `        ``//skip the '?' ` `        ``i++; ` ` `  `        ``//construct the left subtree ` `        ``//Notice after the below recursive call i will point to ':' just before the right child of current node since we pass i by reference ` `        ``root->left = convertExpression(str,i); ` `         `  `        ``//skip the ':' character ` `        ``i++; ` ` `  `        ``//construct the right subtree ` `        ``root->right = convertExpression(str,i); ` `        ``return` `root; ` `    ``} ` `    ``//If the next character is not '?' no subtree just return it ` `    ``else` `return` `root; ` `} ` ` `  `// function print tree ` `void` `printTree( Node *root) ` `{ ` `    ``if` `(!root) ` `        ``return` `; ` `    ``cout << root->data <<``" "``; ` `    ``printTree(root->left); ` `    ``printTree(root->right); ` `} ` ` `  `// Driver program to test above function ` `int` `main() ` `{ ` `    ``string expression = ``"a?b?c:d:e"``; ` `    ``int` `i=0; ` `    ``Node *root = convertExpression(expression, i); ` `    ``printTree(root) ; ` `    ``return` `0; ` `} `

## Java

 `// Java program to convert a ternary  ` `// expreesion to a tree. ` `import` `java.util.Queue; ` `import` `java.util.LinkedList; ` `  `  `// Class to represent Tree node  ` `class` `Node  ` `{ ` `    ``char` `data; ` `    ``Node left, right; ` `  `  `    ``public` `Node(``char` `item)  ` `    ``{ ` `        ``data = item; ` `        ``left = ``null``; ` `        ``right = ``null``; ` `    ``} ` `} ` `  `  `// Class to convert a ternary expression to a Tree  ` `class` `BinaryTree  ` `{ ` `    ``// Function to convert Ternary Expression to a Binary ` `    ``// Tree. It return the root of tree ` `    ``Node convertExpression(``char``[] expression, ``int` `i) ` `    ``{ ` `        ``// Base case ` `        ``if` `(i >= expression.length) ` `            ``return` `null``; ` `      `  `        ``// store current character of expression_string ` `        ``// [ 'a' to 'z'] ` `        ``Node root = ``new` `Node(expression[i]); ` `      `  `        ``// Move ahead in str ` `        ``++i; ` `      `  `        ``// if current character of ternary expression is '?' ` `        ``// then we add next character as a left child of ` `        ``// current node ` `        ``if` `(i < expression.length && expression[i]==``'?'``) ` `            ``root.left = convertExpression(expression, i+``1``); ` `      `  `        ``// else we have to add it as a right child of ` `        ``// current node expression.at(0) == ':' ` `        ``else` `if` `(i < expression.length) ` `            ``root.right = convertExpression(expression, i+``1``); ` `      `  `        ``return` `root; ` `    ``} ` `     `  `    ``// function print tree ` `    ``public` `void` `printTree( Node root) ` `    ``{ ` `        ``if` `(root == ``null``) ` `            ``return``; ` `                 `  `        ``System.out.print(root.data +``" "``); ` `        ``printTree(root.left); ` `        ``printTree(root.right); ` `    ``} ` `     `  `// Driver program to test above function ` `    ``public` `static` `void` `main(String args[])  ` `    ``{ ` `        ``String exp = ``"a?b?c:d:e"``; ` `        ``BinaryTree tree = ``new` `BinaryTree(); ` `        ``char``[] expression=exp.toCharArray();  ` `        ``Node root = tree.convertExpression(expression, ``0``); ` `        ``tree.printTree(root) ; ` `    ``} ` `} ` ` `  `/* This code is contributed by Mr. Somesh Awasthi */`

## Python3

 `# Class to define a node  ` `# structure of the tree ` `class` `Node: ` `    ``def` `__init__(``self``, key): ` `        ``self``.data ``=` `key ` `        ``self``.left ``=` `None` `        ``self``.right ``=` `None` ` `  `# Function to convert ternary  ` `# expression to a Binary tree ` `# It returns the root node  ` `# of the tree ` `def` `convert_expression(expression, i): ` `    ``if` `i >``=` `len``(expression): ` `        ``return` `None` ` `  `    ``# Create a new node object ` `    ``# for the expression at ` `    ``# ith index ` `    ``root ``=` `Node(expression[i]) ` ` `  `    ``i ``+``=` `1` ` `  `    ``# if current character of  ` `    ``# ternary expression is '?' ` `    ``# then we add next character  ` `    ``# as a left child of ` `    ``# current node ` `    ``if` `(i < ``len``(expression) ``and`  `                ``expression[i] ``is` `"?"``): ` `        ``root.left ``=` `convert_expression(expression, i ``+` `1``) ` `         `  `    ``# else we have to add it  ` `    ``# as a right child of ` `    ``# current node expression == ':' ` `    ``elif` `i < ``len``(expression): ` `        ``root.right ``=` `convert_expression(expression, i ``+` `1``) ` `    ``return` `root ` ` `  `# Function to print the tree ` `# in a pre-order traversal pattern ` `def` `print_tree(root): ` `    ``if` `not` `root: ` `        ``return` `    ``print``(root.data, end``=``' '``) ` `    ``print_tree(root.left) ` `    ``print_tree(root.right) ` ` `  `# Driver Code ` `if` `__name__ ``=``=` `"__main__"``: ` `    ``string_expression ``=` `"a?b?c:d:e"` `    ``root_node ``=` `convert_expression(string_expression, ``0``) ` `    ``print_tree(root_node) ` ` `  `# This code is contributed ` `# by Kanav Malhotra `

## C#

 `// C# program to convert a ternary  ` `// expreesion to a tree.  ` `using` `System; ` ` `  `// Class to represent Tree node  ` `public` `class` `Node ` `{ ` `    ``public` `char` `data; ` `    ``public` `Node left, right; ` ` `  `    ``public` `Node(``char` `item) ` `    ``{ ` `        ``data = item; ` `        ``left = ``null``; ` `        ``right = ``null``; ` `    ``} ` `} ` ` `  `// Class to convert a ternary  ` `// expression to a Tree  ` `public` `class` `BinaryTree ` `{ ` `    ``// Function to convert Ternary Expression  ` `    ``// to a Binary Tree. It return the root of tree  ` `    ``public` `virtual` `Node convertExpression(``char``[] expression, ` `                                          ``int` `i) ` `    ``{ ` `        ``// Base case  ` `        ``if` `(i >= expression.Length) ` `        ``{ ` `            ``return` `null``; ` `        ``} ` ` `  `        ``// store current character of  ` `        ``// expression_string [ 'a' to 'z']  ` `        ``Node root = ``new` `Node(expression[i]); ` ` `  `        ``// Move ahead in str  ` `        ``++i; ` ` `  `        ``// if current character of ternary expression  ` `        ``// is '?' then we add next character as a  ` `        ``// left child of current node  ` `        ``if` `(i < expression.Length && expression[i] == ``'?'``) ` `        ``{ ` `            ``root.left = convertExpression(expression, i + 1); ` `        ``} ` ` `  `        ``// else we have to add it as a right child  ` `        ``// of current node expression.at(0) == ':'  ` `        ``else` `if` `(i < expression.Length) ` `        ``{ ` `            ``root.right = convertExpression(expression, i + 1); ` `        ``} ` ` `  `        ``return` `root; ` `    ``} ` ` `  `    ``// function print tree  ` `    ``public` `virtual` `void` `printTree(Node root) ` `    ``{ ` `        ``if` `(root == ``null``) ` `        ``{ ` `            ``return``; ` `        ``} ` ` `  `        ``Console.Write(root.data + ``" "``); ` `        ``printTree(root.left); ` `        ``printTree(root.right); ` `    ``} ` ` `  `// Driver Code ` `public` `static` `void` `Main(``string``[] args) ` `{ ` `    ``string` `exp = ``"a?b?c:d:e"``; ` `    ``BinaryTree tree = ``new` `BinaryTree(); ` `    ``char``[] expression = exp.ToCharArray(); ` `    ``Node root = tree.convertExpression(expression, 0); ` `    ``tree.printTree(root); ` `} ` `} ` ` `  `// This code is contributed by Shrikant13 `

Output :

`a b c d e `

Time Complexity :
O(n) [ here n is length of String ]

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