0572-subtree-of-another-tree.cs

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public bool IsSubtree(TreeNode root, TreeNode subRoot) {
        if (root == null) return root == subRoot;
        if (root.val == subRoot?.val && IsSameTree(root, subRoot)) return true;

        return IsSubtree(root.left, subRoot) || IsSubtree(root.right, subRoot);
    }

    public bool IsSameTree(TreeNode p, TreeNode q) {
        if (p == null || q == null) return p == q;

        return p.val == q.val 
            && IsSameTree(p.left, q.left) 
            && IsSameTree(p.right, q.right);
    }
}