algorithm - Code for checking if a tree is a Binary Search Tree in Java is failing test cases. Unsure why -


i began doing bst problem on hackerrank, should return true if tree is bst, , false otherwise. failing 4 out of 20 total cases , not sure why. person made problem did not provide detail information on how he/she handles inputs , makes tree.

here code:

map<integer, integer> nummap = new hashmap<integer, integer>();       boolean checkduplicates(int val){         if(nummap.containskey(val)){             return false;         }         else{             nummap.put(val, 1);             return true;         }     }       boolean checkbst(node root) {         if(root.left == null && root.right == null){             return (true && checkduplicates(root.data));         }         else if(root.left.data > root.data || root.right.data < root.data){             return false;         }         else{             if(root.left == null){                 return (checkbst(root.right) && checkduplicates(root.data));             }             else if(root.right == null){                 return (checkbst(root.left) && checkduplicates(root.data));             }             else{                 return (checkbst(root.left) && checkbst(root.right) && checkduplicates(root.data));             }         }      }

here link hackerrank problem: https://www.hackerrank.com/challenges/ctci-is-binary-search-tree

what doing wrong/overlooking here?

every node in subtree must smaller/larger root. check root of subtree.

for example not bst:

       5   3       7 1   6

this condition implies there no duplicates, don't have check separately.


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