LeetCode刷题(C++)——Verify Preorder Serialization of a Binary Tree(Medium)
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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) { int position = 1; for(int i=0; i<preorder.size(); ++i){ if(preorder[i]== ','){ preorder[i] = ' '; } } istringstream out(preorder); string str; while(out>>str){ if(--position < 0){ return false; } if(str != "#"){ position += 2; } } return position == 0; }};
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