leetcode 331. Verify Preorder Serialization of a Binary Tree

One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as #.

     _9_    /   \   3     2  / \   / \ 4   1  #  6/ \ / \   / \# # # #   # #

For example, the above binary tree can be serialized to the string "9,3,4,#,#,1,#,#,2,#,6,#,#", where # represents a null node.

Given a string of comma separated values, verify whether it is a correct preorder traversal serialization of a binary tree. Find an algorithm without reconstructing the tree.

Each comma separated value in the string must be either an integer or a character '#' representing null pointer.

You may assume that the input format is always valid, for example it could never contain two consecutive commas such as "1,,3".

Example 1:
"9,3,4,#,#,1,#,#,2,#,6,#,#"
Return true

Example 2:
"1,#"
Return false

Example 3:
"9,#,#,1"
Return false

class Solution {public:bool isValidSerialization(string preorder) {if(preorder.compare("#")==0)return true;int comma=preorder.find_first_of(',');vector<string>quene;while(comma!=string::npos){string str=string(preorder.begin(),preorder.begin()+comma);preorder.erase(preorder.begin(),preorder.begin()+comma+1);comma=preorder.find_first_of(',');//string str2="#";if(str.compare("#")==0){if(quene.size()==1&&preorder.compare("#")==0)return true;else{if(quene.empty())return false;quene.pop_back();}}elsequene.push_back(str);}return false;}};

accepted