[LeetCode By Go 26]606. Construct String from Binary Tree
题目Youneedtoconstructastringconsistsofparenthesisandintegersfromabinarytreewiththepreordertraversingway.Thenullnodeneedstoberepresentedbyemptyparenthesispair"()".Andyouneedtoomitalltheemptyparenthesisp