# Replace each node in binary tree with the sum of its inorder predecessor and successor

Given a binary tree containing n nodes. The problem is to replace each node in the binary tree with the sum of its inorder predecessor and inorder successor.

Examples:

Input :          1
/   \
2     3
/  \  /  \
4   5  6   7

Output :        11
/    \
9      13
/ \    /  \
2   3   4   3

For 1:
Inorder predecessor = 5
Inorder successor  = 6
Sum = 11

For 4:
Inorder predecessor = 0
(as inorder predecessor is not present)
Inorder successor  = 2
Sum = 2

For 7:
Inorder predecessor = 3
Inorder successor  = 0
(as inorder successor is not present)
Sum = 3

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

Approach: Create an array arr. Store 0 at index 0. Now, store the inorder traversal of tree in the array arr. Then, store 0 at last index. 0’s are stored as inorder predecessor of leftmost leaf and inorder successor of rightmost leaf is not present. Now, perform inorder traversal and while traversing node replace node’s value with arr[i-1] + arr[i+1] and then increment i. In the beginning initialize i = 1. For an element arr[i], the values arr[i-1] and arr[i+1] are its inorder predecessor and inorder successor respectively.

## C++

 // C++ implementation to replace each node  // in binary tree with the sum of its inorder  // predecessor and successor #include    using namespace std;    // node of a binary tree struct Node {     int data;     struct Node* left, *right; };    // function to get a new node of a binary tree struct Node* getNode(int data) {     // allocate node     struct Node* new_node =         (struct Node*)malloc(sizeof(struct Node));        // put in the data;     new_node->data = data;     new_node->left = new_node->right = NULL;        return new_node; }    // function to store the inorder traversal // of the binary tree in 'arr' void storeInorderTraversal(struct Node* root,                                  vector& arr) {     // if root is NULL     if (!root)         return;        // first recur on left child     storeInorderTraversal(root->left, arr);        // then store the root's data in 'arr'     arr.push_back(root->data);        // now recur on right child     storeInorderTraversal(root->right, arr); }    // function to replace each node with the sum of its // inorder predecessor and successor void replaceNodeWithSum(struct Node* root,                         vector arr, int* i) {     // if root is NULL     if (!root)         return;        // first recur on left child     replaceNodeWithSum(root->left, arr, i);        // replace node's data with the sum of its     // inorder predecessor and successor     root->data = arr[*i - 1] + arr[*i + 1];        // move 'i' to point to the next 'arr' element     ++*i;        // now recur on right child     replaceNodeWithSum(root->right, arr, i); }    // Utility function to replace each node in binary // tree with the sum of its inorder predecessor  // and successor void replaceNodeWithSumUtil(struct Node* root) {     // if tree is empty     if (!root)         return;        vector arr;        // store the value of inorder predecessor     // for the leftmost leaf     arr.push_back(0);        // store the inoder traversal of the tree in 'arr'     storeInorderTraversal(root, arr);        // store the value of inorder successor     // for the rightmost leaf     arr.push_back(0);          // replace each node with the required sum     int i = 1;     replaceNodeWithSum(root, arr, &i); }    // function to print the preorder traversal // of a binary tree void preorderTraversal(struct Node* root) {     // if root is NULL     if (!root)         return;        // first print the data of node     cout << root->data << " ";        // then recur on left subtree     preorderTraversal(root->left);        // now recur on right subtree     preorderTraversal(root->right); }    // Driver program to test above int main() {     // binary tree formation     struct Node* root = getNode(1); /*         1        */     root->left = getNode(2);        /*       /   \      */     root->right = getNode(3);       /*     2      3     */     root->left->left = getNode(4);  /*    /  \  /   \   */     root->left->right = getNode(5); /*   4   5  6   7   */     root->right->left = getNode(6);     root->right->right = getNode(7);        cout << "Preorder Traversal before tree modification:n";     preorderTraversal(root);        replaceNodeWithSumUtil(root);        cout << "\nPreorder Traversal after tree modification:n";     preorderTraversal(root);        return 0; }

## Java

 // Java implementation to replace each node  // in binary tree with the sum of its inorder  // predecessor and successor import java.util.*; class Solution {        // node of a binary tree static class Node {     int data;      Node left, right; }    //INT class static class INT {     int data; }     // function to get a new node of a binary tree static  Node getNode(int data) {     // allocate node      Node new_node =new Node();         // put in the data;     new_node.data = data;     new_node.left = new_node.right = null;         return new_node; }     // function to store the inorder traversal // of the binary tree in 'arr' static void storeInorderTraversal( Node root,                                  Vector arr) {     // if root is null     if (root==null)         return;         // first recur on left child     storeInorderTraversal(root.left, arr);         // then store the root's data in 'arr'     arr.add(root.data);         // now recur on right child     storeInorderTraversal(root.right, arr); }     // function to replace each node with the sum of its // inorder predecessor and successor static void replaceNodeWithSum( Node root,                         Vector arr, INT i) {     // if root is null     if (root==null)         return;         // first recur on left child     replaceNodeWithSum(root.left, arr, i);         // replace node's data with the sum of its     // inorder predecessor and successor     root.data = arr.get(i.data - 1) + arr.get(i.data + 1);         // move 'i' to point to the next 'arr' element     i.data++;         // now recur on right child     replaceNodeWithSum(root.right, arr, i); }     // Utility function to replace each node in binary // tree with the sum of its inorder predecessor  // and successor static void replaceNodeWithSumUtil( Node root) {     // if tree is empty     if (root==null)         return;         Vector arr= new Vector();         // store the value of inorder predecessor     // for the leftmost leaf     arr.add(0);         // store the inoder traversal of the tree in 'arr'     storeInorderTraversal(root, arr);         // store the value of inorder successor     // for the rightmost leaf     arr.add(0);           // replace each node with the required sum     INT i = new INT();            i.data=1;            replaceNodeWithSum(root, arr, i); }     // function to print the preorder traversal // of a binary tree static void preorderTraversal( Node root) {     // if root is null     if (root==null)         return;         // first print the data of node     System.out.print( root.data + " ");         // then recur on left subtree     preorderTraversal(root.left);         // now recur on right subtree     preorderTraversal(root.right); }     // Driver program to test above public static void main(String args[]) {     // binary tree formation      Node root = getNode(1);       //         1             root.left = getNode(2);        //       /   \           root.right = getNode(3);       //     2      3          root.left.left = getNode(4);  //    /  \  /   \        root.left.right = getNode(5); //   4   5  6   7        root.right.left = getNode(6);     root.right.right = getNode(7);         System.out.println( "Preorder Traversal before tree modification:");     preorderTraversal(root);         replaceNodeWithSumUtil(root);         System.out.println("\nPreorder Traversal after tree modification:");     preorderTraversal(root);     } } //contributed by Arnab Kundu

## Python3

 # Python3 implementation to replace each  # node in binary tree with the sum of its  # inorder predecessor and successor     # class to get a new node of a  # binary tree  class getNode:     def __init__(self, data):                    # put in the data          self.data = data          self.left = self.right = None        # function to store the inorder traversal  # of the binary tree in 'arr'  def storeInorderTraversal(root, arr):            # if root is None      if (not root):         return        # first recur on left child      storeInorderTraversal(root.left, arr)         # then store the root's data in 'arr'      arr.append(root.data)         # now recur on right child      storeInorderTraversal(root.right, arr)    # function to replace each node with the  # sum of its inorder predecessor and successor  def replaceNodeWithSum(root, arr, i):            # if root is None      if (not root):         return        # first recur on left child      replaceNodeWithSum(root.left, arr, i)         # replace node's data with the sum of its      # inorder predecessor and successor      root.data = arr[i[0] - 1] + arr[i[0] + 1]         # move 'i' to poto the next 'arr' element      i[0] += 1        # now recur on right child      replaceNodeWithSum(root.right, arr, i)    # Utility function to replace each node in  # binary tree with the sum of its inorder   # predecessor and successor  def replaceNodeWithSumUtil(root):            # if tree is empty      if (not root):          return        arr = []         # store the value of inorder predecessor      # for the leftmost leaf      arr.append(0)         # store the inoder traversal of the     # tree in 'arr'      storeInorderTraversal(root, arr)         # store the value of inorder successor      # for the rightmost leaf      arr.append(0)         # replace each node with the required sum      i = [1]     replaceNodeWithSum(root, arr, i)    # function to print the preorder traversal  # of a binary tree  def preorderTraversal(root):            # if root is None      if (not root):          return        # first print the data of node      print(root.data, end = " ")        # then recur on left subtree      preorderTraversal(root.left)         # now recur on right subtree      preorderTraversal(root.right)    # Driver Code if __name__ == '__main__':            # binary tree formation      root = getNode(1) #         1          root.left = getNode(2)     #     / \          root.right = getNode(3)     #     2     3          root.left.left = getNode(4) # / \ / \      root.left.right = getNode(5) # 4 5 6 7      root.right.left = getNode(6)      root.right.right = getNode(7)         print("Preorder Traversal before",                   "tree modification:")      preorderTraversal(root)         replaceNodeWithSumUtil(root)      print()     print("Preorder Traversal after",                  "tree modification:")      preorderTraversal(root)    # This code is contributed by PranchalK

## C#

 // C# implementation to replace each  // node in binary tree with the sum  // of its inorder predecessor and successor  using System; using System.Collections.Generic;    class GFG {    // node of a binary tree  public class Node {     public int data;     public Node left, right; }    // INT class  public class INT {     public int data; }    // function to get a new node  // of a binary tree  public static Node getNode(int data) {     // allocate node      Node new_node = new Node();        // put in the data;      new_node.data = data;     new_node.left = new_node.right = null;        return new_node; }    // function to store the inorder traversal  // of the binary tree in 'arr'  public static void storeInorderTraversal(Node root,                                          List arr) {     // if root is null      if (root == null)     {         return;     }        // first recur on left child      storeInorderTraversal(root.left, arr);        // then store the root's data in 'arr'      arr.Add(root.data);        // now recur on right child      storeInorderTraversal(root.right, arr); }    // function to replace each node with  // the sum of its inorder predecessor  // and successor  public static void replaceNodeWithSum(Node root,                                       List arr, INT i) {     // if root is null      if (root == null)     {         return;     }        // first recur on left child      replaceNodeWithSum(root.left, arr, i);        // replace node's data with the      // sum of its inorder predecessor     // and successor      root.data = arr[i.data - 1] + arr[i.data + 1];        // move 'i' to point to the     // next 'arr' element      i.data++;        // now recur on right child      replaceNodeWithSum(root.right, arr, i); }    // Utility function to replace each  // node in binary tree with the sum  // of its inorder predecessor and successor  public static void replaceNodeWithSumUtil(Node root) {     // if tree is empty      if (root == null)     {         return;     }        List arr = new List();        // store the value of inorder     // predecessor for the leftmost leaf      arr.Add(0);        // store the inoder traversal      // of the tree in 'arr'      storeInorderTraversal(root, arr);        // store the value of inorder successor      // for the rightmost leaf      arr.Add(0);        // replace each node with      // the required sum      INT i = new INT();        i.data = 1;        replaceNodeWithSum(root, arr, i); }    // function to print the preorder  // traversal of a binary tree  public static void preorderTraversal(Node root) {     // if root is null      if (root == null)     {         return;     }        // first print the data of node      Console.Write(root.data + " ");        // then recur on left subtree      preorderTraversal(root.left);        // now recur on right subtree      preorderTraversal(root.right); }    // Driver Code public static void Main(string[] args) {     // binary tree formation      Node root = getNode(1); //         1     root.left = getNode(2); //     / \     root.right = getNode(3); //     2     3     root.left.left = getNode(4); // / \ / \     root.left.right = getNode(5); // 4 5 6 7     root.right.left = getNode(6);     root.right.right = getNode(7);        Console.WriteLine("Preorder Traversal " +                  "before tree modification:");     preorderTraversal(root);        replaceNodeWithSumUtil(root);        Console.WriteLine("\nPreorder Traversal after " +                                "tree modification:");     preorderTraversal(root); } }    // This code is contributed by Shrikant13

Output:

Preorder Traversal before tree modification:
1 2 4 5 3 6 7
Preorder Traversal after tree modification:
11 9 2 3 13 4 3

Time Complexity: O(n)
Auxiliary Space: O(n)

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