[Leetcode] Validate Binary Search Tree

Method One: If BST, the order is convenient after the order, increment. It is possible to see if the sequence traversal is incremented to determine

1 classSolution {2      Public:3         BOOLIsvalidbst (TreeNode *root) {4             5             if(Root = =NULL)6                 return true;7vector<int>result;8Stack<treenode*>St;9 Tentreenode* p =Root; One  A             //inorder Traverse -              while(P! = NULL | | st.size ()! =0) -             { the                  while(P! =NULL) -                 { - St.push (p); -p = p->Left ; +                 } -  +                 if(!st.empty ()) A                 { atp =st.top (); - St.pop (); -Result.push_back (p->val); -p = p->Right ; -                 } -             } in              -             //Check if it is Ascend to              for(inti =0; I < result.size ()-1; i++) +             { -                 if(Result[i] < result[i+1]) the                 ; *                 Else $                     return false;Panax Notoginseng             } -             return true; the  +         } A};

Method Two: Using recursion, to determine the current node value, whether in the upper and lower bounds, for the root node, there is no boundary. And then recursive judgment.

1 classSolution {2      Public:3         BOOLIsvalidbst (TreeNode *root) {4             returnIsvalidbst (Root, Int_min, Int_max);5         }   6         BOOLIsvalidbst (TreeNode *root,intMinintmax)7         {   8             if(Root = NULL)return true;9 Ten             if((Root->val < max) && (Root->val > Min) && OneIsvalidbst (root->left, Min, root->val) && AIsvalidbst (Root->right, root->val, max) -               )    -                 return true; the             Else -                 return false; -         }    -};

[Leetcode] Validate Binary Search Tree