Leetcode: validata Binary Search Tree

Leetcode: validata Binary Search Tree

Given a binary tree, determine if it is a valid Binary Search Tree (BST ).

Assume a BST is defined as follows:

• The left subtree of a node contains only nodes with keysLessThe node's key.
• The right subtree of a node contains only nodes with keysGreaterThe node's key.
• Both the left and right Subtrees must also be binary search trees.

Address: https://oj.leetcode.com/problems/validate-binary-search-tree/

Algorithm: In-order traversal to see if the value of the node to be traversed increases progressively. Code:

 1   /*  *  2   * Definition for Binary Tree  3  * Struct treenode {  4   * Int val;  5   * Treenode * left;  6   * Treenode * right;  7   * Treenode (int x): Val (x), left (null), right (null ){}  8   *};  9    */  10   Class  Solution { 11   Public  :  12       Bool Isvalidbst (treenode * Root ){  13           If (! Root) Return   True  ;  14 Stack <treenode *> STK;  15 Treenode * P = Root; 16           While  (P ){  17   STK. Push (P );  18 P = p-> Left;  19   }  20 Treenode * pre = NULL;  21 P = NULL;  22           While (!STK. Empty ()){  23 Pre = P;  24 P = STK. Top ();  25   STK. Pop ();  26               If (Pre & P-> Val <= pre-> Val ){  27                   Return   False  ;  28  }  29               If (P-> Right ){  30 Treenode * q = p-> Right;  31                   While  (Q ){  32   STK. Push (Q );  33 Q = Q-> Left;  34   } 35   }  36   }  37           Return   True  ;  38   }  39 };

 

Leetcode: validata Binary Search Tree