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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
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150 / 150 test cases passed.
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Status:
Accepted |
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Runtime: 8 ms
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1 class Solution { 2 public: 3 bool isValidSerialization(string preorder) { 4 int l = preorder.length(); 5 if(preorder[0] == ‘#‘){ 6 if(l == 1) return true; 7 else return false; 8 } 9 int i = 0; 10 stack<int> s; 11 s.push(0); 12 while(i<l && preorder[i] != ‘,‘) i++; 13 i++; 14 int te; 15 while(i < l) 16 { 17 if(preorder[i] == ‘#‘){ 18 if(s.empty() == 1) return false; 19 while(!s.empty()) 20 { 21 te = s.top(); 22 if(te == 2) return false; 23 s.pop(); 24 s.push(te + 1); 25 te = s.top(); 26 if(te == 1){ 27 break; 28 } 29 if(te == 2 ){ 30 s.pop(); 31 } 32 } 33 if(s.empty() == 1 && i < l - 1) return false; 34 } 35 else{ 36 s.push(0); 37 } 38 while(i < l && preorder[i] != ‘,‘) i++; 39 i++; 40 } 41 if(s.size() == 0) return true; 42 return false; 43 } 44 };
leetcode 331. Verify Preorder Serialization of a Binary Tree
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原文地址：http://www.cnblogs.com/njczy2010/p/5449690.html
