LeetCode 572. Subtree of Another Tree

Question

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.

https://leetcode.com/problems/subtree-of-another-tree/

• Solution1

class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if (s == null && t == null) return true;
        if (s == null) return false;
        if (isSame(s, t)) return true;
        return isSubtree(s.left, t) || isSubtree(s.right, t);
    }
    private boolean isSame(TreeNode s, TreeNode t) {
        if (s == null && t == null) return true;
        if (s == null || t == null) return false;
        if (s.val != t.val) return false;
        return isSame(s.left, t.left) && isSame(s.right, t.right);
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)