The sword refers to offer 23. Sequential traversal sequence of binary search tree (binary search tree)

Title Description

Enter an array of integers to determine if the array is the result of a sequential traversal of a binary search tree. If yes, output yes, otherwise output No. Assume that any two digits of the input array are different.

Title Address

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Ideas

Ideas:

Take [5,7,6,9,11,10,8] as an example, the last digit of the post-order traversal result 8 is the value of the root node, in which the first three digits 5, 7, and 6 are smaller than 8, the left subtree node of the node with a value of 8, and the next three digits 9, 11, and 10 are larger than 8, which is the right subtree of the node with a value of 8.

Using the same method to determine the structure of the sub-tree corresponding to each part of the array, this is actually a recursive process, for the sequence 5,7,6, the last number 6 is the Zuozi root node value, the number 5:6 is small, is a value of 6 node left Dial hand node, and 7 is its right child node. Similarly, in sequences 9, 11, 10, the last Number 10 is the root node of the right subtree, the number 9:10 is small, is the node with a value of 10 left Dial hand node, and 11 is its right child node.

Using the recursive method, the Saozi of the right subtree of the array is determined first, and the left subtree is located. Determine if the right subtree is a binary search tree.

Python

#-*-coding:utf-8-*-classSolution:defVerifysquenceofbst (self, sequence):#Write code here        ifLen (sequence) = =0:returnFalseifLen (sequence) = = 1:            returnTrue Root= Sequence[-1]#Get root nodei =0 whileSequence[i] < root:#left dial hand treei + = 1k=I forIinchRange (K,len (sequence)):ifSequence[i] <= Root:#Judging right sub-tree                returnFalse Left_k=Sequence[:k] Right_k= Sequence[k:len (Sequence)-1] left, right=true, TrueifLen (Left_k) >0:left=Self . Verifysquenceofbst (Left_k)ifLen (Right_k) >0:right=Self . Verifysquenceofbst (Right_k)returnLeft and Rightif __name__=='__main__': Sequence= [4,6,5,9,11,10,8] Result=solution (). VERIFYSQUENCEOFBST (Sequence)Print(Result)

The sword refers to offer 23. Sequential traversal sequence of binary search tree (binary search tree)