树的子结构问题

public class Solution {
    public boolean HasSubtree(TreeNode root1,TreeNode root2) {
        return ((root1 != null && root2 != null) && (recur(root1,root2) 
                 || HasSubtree(root1.left,root2) || HasSubtree(root1.right,root2)));
    }
    public boolean recur(TreeNode root1,TreeNode root2){
        if(root2 == null) return true;
        if(root1 == null || root1.val != root2.val) return false;
        return recur(root1.left,root2.left) && recur(root1.right,root2.right);
    }
}