Check if a binary tree is subtree of another binary tree | Set 1

Given two binary trees, check if the first tree is subtree of the second one. A subtree of a tree T is a tree S consisting of a node in T and all of its descendants in T. The subtree corresponding to the root node is the entire tree; the subtree corresponding to any other node is called a proper subtree.

For example, in the following case, tree S is a subtree of tree T.

        Tree 2
          10  
        /    \ 
      4       6
       \
        30


        Tree 1
              26
            /   \
          10     3
        /    \     \
      4       6      3
       \
        30


Solution: Traverse the tree T in preorder fashion. For every visited node in the traversal, see if the subtree rooted with this node is identical to S.

Following is the implementation for this.

C

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#include <stdio.h>
#include <stdlib.h>
  
/* A binary tree node has data, left child and right child */
struct node
{
    int data;
    struct node* left;
    struct node* right;
};
  
/* A utility function to check whether trees with roots as root1 and
   root2 are identical or not */
bool areIdentical(struct node * root1, struct node *root2)
{
    /* base cases */
    if (root1 == NULL && root2 == NULL)
        return true;
  
    if (root1 == NULL || root2 == NULL)
        return false;
  
    /* Check if the data of both roots is same and data of left and right
       subtrees are also same */
    return (root1->data == root2->data   &&
            areIdentical(root1->left, root2->left) &&
            areIdentical(root1->right, root2->right) );
}
  
  
/* This function returns true if S is a subtree of T, otherwise false */
bool isSubtree(struct node *T, struct node *S)
{
    /* base cases */
    if (S == NULL)
        return true;
  
    if (T == NULL)
        return false;
  
    /* Check the tree with root as current node */
    if (areIdentical(T, S))
        return true;
  
    /* If the tree with root as current node doesn't match then
       try left and right subtrees one by one */
    return isSubtree(T->left, S) ||
           isSubtree(T->right, S);
}
  
  
/* 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 function */
int main()
{
    // TREE 1
    /* Construct the following tree
              26
            /   \
          10     3
        /    \     \
      4      6      3
       \
        30
    */
    struct node *T        = newNode(26);
    T->right              = newNode(3);
    T->right->right       = newNode(3);
    T->left               = newNode(10);
    T->left->left         = newNode(4);
    T->left->left->right  = newNode(30);
    T->left->right        = newNode(6);
  
    // TREE 2
    /* Construct the following tree
          10
        /    \
      4      6
       \
        30
    */
    struct node *S    = newNode(10);
    S->right          = newNode(6);
    S->left           = newNode(4);
    S->left->right    = newNode(30);
  
  
    if (isSubtree(T, S))
        printf("Tree 2 is subtree of Tree 1");
    else
        printf("Tree 2 is not a subtree of Tree 1");
  
    getchar();
    return 0;
}

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Java

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// Java program to check if binary tree is subtree of another binary tree
   
// A binary tree node
class Node 
{
    int data;
    Node left, right, nextRight;
   
    Node(int item) 
    {
        data = item;
        left = right = nextRight = null;
    }
}
   
class BinaryTree 
{
    Node root1,root2;
   
    /* A utility function to check whether trees with roots as root1 and
       root2 are identical or not */
    boolean areIdentical(Node root1, Node root2) 
    {
   
        /* base cases */
        if (root1 == null && root2 == null)
            return true;
   
        if (root1 == null || root2 == null)
            return false;
   
        /* Check if the data of both roots is same and data of left and right
           subtrees are also same */
        return (root1.data == root2.data
                && areIdentical(root1.left, root2.left)
                && areIdentical(root1.right, root2.right));
    }
   
    /* This function returns true if S is a subtree of T, otherwise false */
    boolean isSubtree(Node T, Node S) 
    {
        /* base cases */
        if (S == null
            return true;
   
        if (T == null)
            return false;
   
        /* Check the tree with root as current node */
        if (areIdentical(T, S)) 
            return true;
   
        /* If the tree with root as current node doesn't match then
           try left and right subtrees one by one */
        return isSubtree(T.left, S)
                || isSubtree(T.right, S);
    }
   
    public static void main(String args[]) 
    {
        BinaryTree tree = new BinaryTree();
           
        // TREE 1
        /* Construct the following tree
              26
             /   \
            10     3
           /    \     \
          4      6      3
           \
            30  */
            
        tree.root1 = new Node(26);
        tree.root1.right = new Node(3);
        tree.root1.right.right = new Node(3);
        tree.root1.left = new Node(10);
        tree.root1.left.left = new Node(4);
        tree.root1.left.left.right = new Node(30);
        tree.root1.left.right = new Node(6);
   
        // TREE 2
        /* Construct the following tree
           10
         /    \
         4      6
          \
          30  */
            
        tree.root2 = new Node(10);
        tree.root2.right = new Node(6);
        tree.root2.left = new Node(4);
        tree.root2.left.right = new Node(30);
   
        if (tree.isSubtree(tree.root1, tree.root2))
            System.out.println("Tree 2 is subtree of Tree 1 ");
        else
            System.out.println("Tree 2 is not a subtree of Tree 1");
    }
}
   
// This code has been contributed by Mayank Jaiswal

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Python

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# Python program to check binary tree is a subtree of 
# another 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
  
# A utility function to check whether trees with roots
# as root 1 and root2 are indetical or not
def areIdentical(root1, root2):
      
    # Base Case
    if root1 is None and root2 is None:
        return True
    if root1 is None or root2 is None:
        return False
  
    # Check fi the data of both roots is same and data of
    # left and right subtrees are also same
    return (root1.data == root2.data and 
            areIdentical(root1.left , root2.left)and
            areIdentical(root1.right, root2.right)
            
  
# This function returns True if S is a subtree of T,
# otherwise False
def isSubtree(T, S):
      
    # Base Case
    if S is None:
        return True
  
    if T is None:
        return False
  
    # Check the tree with root as current node
    if (areIdentical(T, S)):
        return True
  
    # IF the tree with root as current node doesn't match
    # then try left and right subtreee one by one
    return isSubtree(T.left, S) or isSubtree(T.right, S)
  
  
# Driver program to test above function
  
""" TREE 1
     Construct the following tree
              26
            /   \
          10     3
        /    \     \
      4      6      3
       \
        30
    """
  
T = Node(26)
T.right = Node(3)
T.right.right  = Node(3)
T.left = Node(10)
T.left.left = Node(4)
T.left.left.right = Node(30)
T.left.right = Node(6)
  
""" TREE 2
     Construct the following tree
          10
        /    \
      4      6
       \
        30
    """
S = Node(10)
S.right = Node(6)
S.left = Node(4)
S.left.right = Node(30)
  
if isSubtree(T, S):
    print "Tree 2 is subtree of Tree 1"
else :
    print "Tree 2 is not a subtree of Tree 1"
  
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

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Output:

Tree 2 is subtree of Tree 1 

Time Complexity: Time worst case complexity of above solution is O(mn) where m and n are number of nodes in given two trees.

We can solve the above problem in O(n) time. Please refer Check if a binary tree is subtree of another binary tree | Set 2 for O(n) solution.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



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Improved By : SrivathsanAravamudan