# Sum of nodes in the left view of the given binary tree

Given a binary tree, the task is to find the sum of the nodes which are visible in the left view. The left view of a binary tree is the set of nodes visible when the tree is viewed from the left.

Examples:

```Input:
1
/  \
2    3
/ \    \
4   5    6
Output: 7
1 + 2 + 4 = 7

Input:
1
/  \
2      3
\
4
\
5
\
6
Output: 18
```

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

Approach: The problem can be solved using simple recursive traversal. We can keep track of the level of a node by passing a parameter to all the recursive calls. The idea is to keep track of the maximum level also and traverse the tree in a manner that the left subtree is visited before the right subtree. Whenever a node whose level is more than the maximum level so far is encountered, add the value of the node to the sum because it is the first node in its level (Note that the left subtree is traversed before the right subtree).

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `class` `Node { ` `public``: ` `    ``int` `data; ` `    ``Node *left, *right; ` `}; ` ` `  `// A utility function to create ` `// a new Binary Tree Node ` `Node* newNode(``int` `item) ` `{ ` `    ``Node* temp = ``new` `Node(); ` `    ``temp->data = item; ` `    ``temp->left = temp->right = NULL; ` `    ``return` `temp; ` `} ` ` `  `// Recursive function to find the sum of nodes ` `// of the left view of the given binary tree ` `void` `sumLeftViewUtil(Node* root, ``int` `level, ``int``* max_level, ``int``* sum) ` `{ ` `    ``// Base Case ` `    ``if` `(root == NULL) ` `        ``return``; ` ` `  `    ``// If this is the first Node of its level ` `    ``if` `(*max_level < level) { ` `        ``*sum += root->data; ` `        ``*max_level = level; ` `    ``} ` ` `  `    ``// Recur for left and right subtrees ` `    ``sumLeftViewUtil(root->left, level + 1, max_level, sum); ` `    ``sumLeftViewUtil(root->right, level + 1, max_level, sum); ` `} ` ` `  `// A wrapper over sumLeftViewUtil() ` `void` `sumLeftView(Node* root) ` `{ ` `    ``int` `max_level = 0; ` `    ``int` `sum = 0; ` `    ``sumLeftViewUtil(root, 1, &max_level, &sum); ` `    ``cout << sum; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``Node* root = newNode(12); ` `    ``root->left = newNode(10); ` `    ``root->right = newNode(30); ` `    ``root->right->left = newNode(25); ` `    ``root->right->right = newNode(40); ` ` `  `    ``sumLeftView(root); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach ` ` `  `// Class for a node of the tree ` `class` `Node { ` `    ``int` `data; ` `    ``Node left, right; ` ` `  `    ``public` `Node(``int` `item) ` `    ``{ ` `        ``data = item; ` `        ``left = right = ``null``; ` `    ``} ` `} ` ` `  `class` `BinaryTree { ` `    ``Node root; ` `    ``static` `int` `max_level = ``0``; ` `    ``static` `int` `sum = ``0``; ` ` `  `    ``// Recursive function to find the sum of nodes ` `    ``// of the left view of the given binary tree ` `    ``void` `sumLeftViewUtil(Node node, ``int` `level) ` `    ``{ ` `        ``// Base Case ` `        ``if` `(node == ``null``) ` `            ``return``; ` ` `  `        ``// If this is the first node of its level ` `        ``if` `(max_level < level) { ` `            ``sum += node.data; ` `            ``max_level = level; ` `        ``} ` ` `  `        ``// Recur for left and right subtrees ` `        ``sumLeftViewUtil(node.left, level + ``1``); ` `        ``sumLeftViewUtil(node.right, level + ``1``); ` `    ``} ` ` `  `    ``// A wrapper over sumLeftViewUtil() ` `    ``void` `sumLeftView() ` `    ``{ ` ` `  `        ``sumLeftViewUtil(root, ``1``); ` `        ``System.out.print(sum); ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String args[]) ` `    ``{ ` `        ``BinaryTree tree = ``new` `BinaryTree(); ` `        ``tree.root = ``new` `Node(``12``); ` `        ``tree.root.left = ``new` `Node(``10``); ` `        ``tree.root.right = ``new` `Node(``30``); ` `        ``tree.root.right.left = ``new` `Node(``25``); ` `        ``tree.root.right.right = ``new` `Node(``40``); ` ` `  `        ``tree.sumLeftView(); ` `    ``} ` `} `

## Python3

 `# Python3 implementation of the approach ` ` `  `# A binary tree node  ` `class` `Node:  ` ` `  `    ``# Constructor to create a new node  ` `    ``def` `__init__(``self``, data):  ` `        ``self``.data ``=` `data  ` `        ``self``.left ``=` `None` `        ``self``.right ``=` `None` ` `  ` `  `# Recursive function to find the sum of nodes  ` `# of the left view of the given binary tree ` `def` `sumLeftViewUtil(root, level, max_level, ``sum``):  ` `     `  `    ``# Base Case  ` `    ``if` `root ``is` `None``:  ` `        ``return` ` `  `    ``# If this is the first node of its level  ` `    ``if` `(max_level[``0``] < level):  ` `        ``sum``[``0``]``+``=` `root.data  ` `        ``max_level[``0``] ``=` `level  ` ` `  `    ``# Recur for left and right subtree  ` `    ``sumLeftViewUtil(root.left, level ``+` `1``, max_level, ``sum``)  ` `    ``sumLeftViewUtil(root.right, level ``+` `1``, max_level, ``sum``)  ` ` `  ` `  `# A wrapper over sumLeftViewUtil()  ` `def` `sumLeftView(root):  ` `    ``max_level ``=` `[``0``]  ` `    ``sum` `=``[``0``] ` `    ``sumLeftViewUtil(root, ``1``, max_level, ``sum``)  ` `    ``print``(``sum``[``0``]) ` ` `  ` `  `# Driver code ` `root ``=` `Node(``12``)  ` `root.left ``=` `Node(``10``)  ` `root.right ``=` `Node(``20``)  ` `root.right.left ``=` `Node(``25``)  ` `root.right.right ``=` `Node(``40``)  ` `sumLeftView(root) `

## C#

 `// C# implementation of the approach ` `using` `System; ` ` `  `// Class for a node of the tree ` `public` `class` `Node { ` `    ``public` `int` `data; ` `    ``public` `Node left, right; ` ` `  `    ``public` `Node(``int` `item) ` `    ``{ ` `        ``data = item; ` `        ``left = right = ``null``; ` `    ``} ` `} ` ` `  `public` `class` `BinaryTree { ` `    ``public` `Node root; ` `    ``public` `static` `int` `max_level = 0; ` `    ``public` `static` `int` `sum = 0; ` ` `  `    ``// Recursive function to find the sum of nodes ` `    ``// of the left view of the given binary tree ` `    ``public` `virtual` `void` `leftViewUtil(Node node, ``int` `level) ` `    ``{ ` `        ``// Base Case ` `        ``if` `(node == ``null``) { ` `            ``return``; ` `        ``} ` ` `  `        ``// If this is the first node of its level ` `        ``if` `(max_level < level) { ` `            ``sum += node.data; ` `            ``max_level = level; ` `        ``} ` ` `  `        ``// Recur for left and right subtrees ` `        ``leftViewUtil(node.left, level + 1); ` `        ``leftViewUtil(node.right, level + 1); ` `    ``} ` ` `  `    ``// A wrapper over leftViewUtil() ` `    ``public` `virtual` `void` `leftView() ` `    ``{ ` `        ``leftViewUtil(root, 1); ` `        ``Console.Write(sum); ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main(``string``[] args) ` `    ``{ ` `        ``BinaryTree tree = ``new` `BinaryTree(); ` `        ``tree.root = ``new` `Node(12); ` `        ``tree.root.left = ``new` `Node(10); ` `        ``tree.root.right = ``new` `Node(30); ` `        ``tree.root.right.left = ``new` `Node(25); ` `        ``tree.root.right.right = ``new` `Node(40); ` ` `  `        ``tree.leftView(); ` `    ``} ` `} `

Output:

```47
```

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