Leetcode 331. Verify preorder serialization of a Binary Tree

Transmission Door

331. Verify preorder serialization of a Binary TreeMy SubmissionsQuestionEditorial SolutionTotal accepted:10790 Total submissions:34071 difficulty:medium

One-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 "9,3,4,#,#,1,#,#,2,#,6,#,#" is serialized to the string, 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 is either an integer or a character ‘#‘ representing null pointer.

Assume that the input format is always valid, for example it could never contain, consecutive commas such as .

Example 1:
"9,3,4,#,#,1,#,#,2,#,6,#,#"
Returntrue

Example 2:
"1,#"
Returnfalse

Example 3:
"9,#,#,1"
Returnfalse

Test instructions: Judging the given string is not a valid pre-order traversal idea: with a stack, if a node's Saozi right subtree is true, the node returns true False if the condition: 1. A node has been traversed by both the left and right subtrees, followed by the son of the node (e.g. 1,#,#,#) 2. The root node is the end of the access, followed by other nodes (#,1 or 1,#,#,1)

150/150 Test cases passed.	status:accepted
Runtime:8 ms

1 classSolution {2  Public:3     BOOLIsvalidserialization (stringpreorder) {4         intL =preorder.length ();5         if(preorder[0] =='#'){6             if(L = =1)return true;7             Else return false;8         }9         inti =0;Tenstack<int>s; OneS.push (0); A          while(I<l && preorder[i]! =',') i++; -i++; -         intte; the          while(I <l) -         { -             if(Preorder[i] = ='#'){ -                 if(S.empty () = =1)return false; +                  while(!s.empty ()) -                 { +Te =s.top (); A                     if(Te = =2)return false; at S.pop (); -S.push (Te +1); -Te =s.top (); -                     if(Te = =1){ -                          Break; -                     } in                     if(Te = =2 ){ - S.pop (); to                     } +                 } -                 if(S.empty () = =1&& I < L-1)return false; the             } *             Else{ $S.push (0);Panax Notoginseng             } -              while(I < L && Preorder[i]! =',') i++; thei++; +         } A         if(s.size () = =0)return true; the         return false; +     } -};

Leetcode 331. Verify preorder serialization of a Binary Tree