6. Subtree of Another Tree

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise.

A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node’s descendants. The tree tree could also be considered as a subtree of itself.

Example 1:

Input: root = [3,4,5,1,2], subRoot = [4,1,2]
Output: true

Example 2:

Input: root = [3,4,5,1,2,null,null,null,null,0], subRoot =[4,1,2]
Output: false

Constraints:

• The number of nodes in the root tree is in the range [1, 2000].
• The number of nodes in the subRoot tree is in the range [1, 1000].
• -104 <= root.val <= 104
• -104 <= subRoot.val <= 104

Approach - Recursion

• Time: O(m*n) Space: O(m+n)

class Solution {
    public boolean isSubtree(TreeNode root, TreeNode subRoot) {
        if (subRoot == null) return true;
        if (root == null) return false;
        if (same(root,subRoot)) return true;
        return isSubtree(root.left,subRoot) || isSubtree(root.right,subRoot);
    }
 
    public boolean same(TreeNode a, TreeNode b) {
        if (a == null && b == null) return true;
 
        if (a != null && b != null && a.val == b.val) 
            return same(a.left,b.left) && same(a.right,b.right);
        return false;    
    }
}