Print Ancestors of a given node in Binary Tree

Given a Binary Tree and a key, write a function that prints all the ancestors of the key in the given binary tree. 

For example, if the given tree is following Binary Tree and the key is 7, then your function should print 4, 2, and 1.

              1
            /   \
          2      3
        /  \
      4     5
     /
    7

Thanks to Mike, Sambasiva and wgpshashank for their contribution.

C++

// C++ program to print ancestors of given node
#include<bits/stdc++.h>

using namespace std;

/* A binary tree node has data, pointer to left child
   and a pointer to right child */
struct node
{
   int data;
   struct node* left;
   struct node* right;
};

/* If target is present in tree, then prints the ancestors
   and returns true, otherwise returns false. */
bool printAncestors(struct node *root, int target)
{
  /* base cases */
  if (root == NULL)
     return false;

  if (root->data == target)
     return true;

  /* If target is present in either left or right subtree of this node,
     then print this node */
  if ( printAncestors(root->left, target) ||
       printAncestors(root->right, target) )
  {
    cout << root->data << " ";
    return true;
  }

  /* Else return false */
  return false;
}

/* Helper function that allocates a new node with the
   given data and NULL left and right pointers. */
struct node* newnode(int data)
{
  struct node* node = (struct node*)
                       malloc(sizeof(struct node));
  node->data = data;
  node->left = NULL;
  node->right = NULL;

  return(node);
}

/* Driver program to test above functions*/
int main()
{

  /* Construct the following binary tree
              1
            /   \
          2      3
        /  \
      4     5
     /
    7
  */
  struct node *root = newnode(1);
  root->left        = newnode(2);
  root->right       = newnode(3);
  root->left->left  = newnode(4);
  root->left->right = newnode(5);
  root->left->left->left  = newnode(7);

  printAncestors(root, 7);

  getchar();
  return 0;
}

Java

// Java program to print ancestors of given node

/* A binary tree node has data, pointer to left child
   and a pointer to right child */
class Node
{
    int data;
    Node left, right, nextRight;

    Node(int item)
    {
        data = item;
        left = right = nextRight = null;
    }
}

class BinaryTree
{
    Node root;

    /* If target is present in tree, then prints the ancestors
       and returns true, otherwise returns false. */
    boolean printAncestors(Node node, int target)
    {
         /* base cases */
        if (node == null)
            return false;

        if (node.data == target)
            return true;

        /* If target is present in either left or right subtree
           of this node, then print this node */
        if (printAncestors(node.left, target)
                || printAncestors(node.right, target))
        {
            System.out.print(node.data + " ");
            return true;
        }

        /* Else return false */
        return false;
    }

    /* Driver program to test above functions */
    public static void main(String args[])
    {
        BinaryTree tree = new BinaryTree();

        /* Construct the following binary tree
                  1
                /   \
               2     3
              /  \
             4    5
            /
           7
        */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.left.left.left = new Node(7);

        tree.printAncestors(tree.root, 7);

    }
}

// This code has been contributed by Mayank Jaiswal

Python3

# Python program to print ancestors of given node in
# binary tree

# 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

# If target is present in tree, then prints the ancestors
# and returns true, otherwise returns false
def printAncestors(root, target):

    # Base case
    if root == None:
        return False

    if root.data == target:
        return True

    # If target is present in either left or right subtree
    # of this node, then print this node
    if (printAncestors(root.left, target) or
        printAncestors(root.right, target)):
        print(root.data,end=' ')
        return True

    # Else return False
    return False

# Driver program to test above function
root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.right = Node(5)
root.left.left.left = Node(7)

printAncestors(root, 7)

# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

C#

using System;

// C# program to print ancestors of given node

/* A binary tree node has data, pointer to left child
and a pointer to right child */
public class Node
{
    public int data;
    public Node left, right, nextRight;

    public Node(int item)
    {
        data = item;
        left = right = nextRight = null;
    }
}

public class BinaryTree
{
    public Node root;

    /* If target is present in tree, then prints the ancestors
    and returns true, otherwise returns false. */
    public virtual bool printAncestors(Node node, int target)
    {
        /* base cases */
        if (node == null)
        {
            return false;
        }

        if (node.data == target)
        {
            return true;
        }

        /* If target is present in either left or right subtree
        of this node, then print this node */
        if (printAncestors(node.left, target)
        || printAncestors(node.right, target))
        {
            Console.Write(node.data + " ");
            return true;
        }

        /* Else return false */
        return false;
    }

    /* Driver program to test above functions */
    public static void Main(string[] args)
    {
        BinaryTree tree = new BinaryTree();

        /* Construct the following binary tree
                1
                / \
            2     3
            / \
            4 5
            /
        7
        */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.left.left.left = new Node(7);

        tree.printAncestors(tree.root, 7);

    }
}

// This code is contributed by Shrikant13

Javascript

<script>

    // JavaScript program to print ancestors of given node

    class Node
    {
        constructor(item) {
              this.data = item;
            this.left = null;
            this.right = null;
            this.nextRight = null;
        }
    }

    let root;

    /* If target is present in tree, then prints the ancestors
       and returns true, otherwise returns false. */
    function printAncestors(node, target)
    {
         /* base cases */
        if (node == null)
            return false;

        if (node.data == target)
            return true;

        /* If target is present in either left or right subtree
           of this node, then print this node */
        if (printAncestors(node.left, target)
                || printAncestors(node.right, target))
        {
            document.write(node.data + " ");
            return true;
        }

        /* Else return false */
        return false;
    }

    /* Construct the following binary tree
                    1
                  /   \
                 2     3
                /  \
               4    5
              /
             7
          */
    root = new Node(1);
    root.left = new Node(2);
    root.right = new Node(3);
    root.left.left = new Node(4);
    root.left.right = new Node(5);
    root.left.left.left = new Node(7);

    printAncestors(root, 7);

</script>

Output

4 2 1 

Time Complexity: O(n) where n is the number of nodes in the given Binary Tree.
Auxiliary Space: O(h) where h is the height of given Binary Tree

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