[Leetcode] Binary Tree Zigzag level Order traversal

To being honest, I do not know whether this problem are designed to let you use stacks. Anyway, I don ' t. Here is my codes, both BFS and DFS version.

1     //BFS2vector<vector<int>> Zigzaglevelorder (treenode*root) {3vector<vector<int> >levels;4         if(!root)returnlevels;5Queue<treenode*>tovisit;6 Tovisit.push (root);7         intCurlevelnodes =1;8         BOOLFlag =false;9          while(!Tovisit.empty ()) {Tenvector<int>Level ; One              for(inti =0; i < curlevelnodes; i++) { Atreenode* node =Tovisit.front (); - Tovisit.pop (); -Level.push_back (Node-val); the                 if(node-to-left) Tovisit.push (node-Left ); -                 if(node-right) Tovisit.push (node-Right ); -             } -             if(flag) { + Reverse (Level.begin (), Level.end ()); -Flag =false; +             } A             ElseFlag =true; at levels.push_back (level); -Curlevelnodes =tovisit.size (); -         } -         returnlevels; -     } -  in     //DFS -     voidDFS (treenode* node,intCurlevel,BOOL& Nextlevel, vector<int>&Level ) { to         if(!node)return; +         if(Curlevel = =1) { -Level.push_back (Node-val); the             if(Node-left | | node-right) Nextlevel =true; *         } $         Else {Panax NotoginsengDFS (node-left, Curlevel-1, Nextlevel, level); -DFS (node-right, Curlevel-1, Nextlevel, level); the         } +     } Avector<vector<int> > Zigzaglevelorder (treenode*root) { thevector<vector<int> >levels; +         if(!root)returnlevels; -         intCurlevel =1; $         BOOLNextlevel =true, flag =false; $          while(nextlevel) { -Nextlevel =false; -vector<int>Level ; theDFS (Root, curlevel++, Nextlevel, level); -             if(flag) {Wuyi Reverse (Level.begin (), Level.end ()); theFlag =false; -             }  Wu             ElseFlag =true; - levels.push_back (level); About         } $         returnlevels; -}

Update

Thanks to the remind of Ljdsoft1, I had rewritten the code to traverse the nodes in Ziazag-order instead of simply revers ing it. The code is as follows, using the stacks.

1 classSolution {2  Public:3vector<vector<int>> Zigzaglevelorder (treenode*root) {4vector<vector<int> >levels;5         if(!root)returnlevels;6Stack<treenode*>Curlevel, Nextlevel;7 Curlevel.push (root);8         BOOLReversed =false;9          while(!Curlevel.empty ()) { Tenvector<int>Level ; One              while(!Curlevel.empty ()) { Atreenode* node =curlevel.top (); - Curlevel.pop (); -Level.push_back (Node-val); the                 if(reversed) { -                     if(node-right) Nextlevel.push (node-Right ); -                     if(node-to-left) Nextlevel.push (node-Left ); -                 } +                 Else { -                     if(node-to-left) Nextlevel.push (node-Left ); +                     if(node-right) Nextlevel.push (node-Right ); A                 } at             } - levels.push_back (level); - swap (Curlevel, nextlevel); -Reversed =!reversed; -         } -         returnlevels; in     } -};

[Leetcode] Binary Tree Zigzag level Order traversal