task5

// n - count of nodes in tree `s`,
// m - count of nodes in tree `t`.
// O(n * m) - time complexity,
// O(n) - space complexity.
class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        return s != null && (isEquals(s, t) || isSubtree(s.left, t) || isSubtree(s.right, t));
    }

    private boolean isEquals(TreeNode s, TreeNode t) {
        if (s == null && t == null) {
            return true;
        }
        if (s == null || t == null) {
            return false;
        }
        return s.val == t.val && isEquals(s.left, t.left) && isEquals(s.right, t.right);
    }
}