572. Subtree of Another Tree

Problem

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].

• -10^4 <= root.val <= 10^4

• -10^4 <= subRoot.val <= 10^4

Solution (Java)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private boolean isSubtreeFound(TreeNode root, TreeNode subRoot) {
        if (root == null && subRoot == null) {
            return true;
        }
        if (root == null || subRoot == null) {
            return false;
        }
        if (root.val == subRoot.val) {
            return isSubtreeFound(root.left, subRoot.left) && isSubtree(root.right, subRoot.right);
        } else {
            return false;
        }
    }

    public boolean isSubtree(TreeNode root, TreeNode subRoot) {
        if (root == null && subRoot == null) {
            return true;
        }
        if (root == null || subRoot == null) {
            return false;
        }
        return isSubtreeFound(root, subRoot)
                || isSubtree(root.left, subRoot)
                || isSubtree(root.right, subRoot);
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).