199. Binary Tree Right Side View (Tree, Stack)

Given A binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered From top to bottom.

For example:
Given The following binary tree,

1 <---
/   \
2 3 <---
\     \
5 4 <---

You should return [1, 3, 4].

The following is not a good idea, but also consider the portion of the left subtree that is longer than the right sub-tree

/** Definition for a binary tree node. * struct TreeNode {* int val; * TreeNode *left; * TreeNode *right; * TreeNode (int x): Val (x), left (null), right (NULL) {} *}; */classSolution { Public: Vector<int> Rightsideview (treenode*root) {Vector<int>ret; TreeNode* current =Root;  while(current) {Ret.push_back ( current-val); if(current->right) Current = Current->Right ; ElseCurrent = Current->Left ; }        returnret; }};

Result:wrong Answer

Input: [1,2,3,4]
Output: [1,3]
Expected: [1,3,4]

So, you have to use stack to record the subtree on the left.

/** Definition for a binary tree node. * struct TreeNode {* int val; * TreeNode *left; * TreeNode *right; * TreeNode (int x): Val (x), left (null), right (NULL) {} *}; */classSolution { Public: Vector<int> Rightsideview (treenode*root) {Vector<int>ret; TreeNode* current =Root; intdepth =0;//depth so far        intDepthgap; Stack<TreeNode*>Nodestack; Stack<int>Depthstack;  while(current) {Ret.push_back ( current-val); Depth++; if(current->Right ) {                if(current->Left ) {Nodestack.push ( current-Left );                Depthstack.push (depth); } Current= current->Right ; }             Else{ Current= current->Left ; }        }                 while(!Nodestack.empty ()) { Current=Nodestack.top ();            Nodestack.pop (); Depthgap= Depth-Depthstack.top ();            Depthstack.pop ();  while(depthgap) {Depthgap--; if(current->Right ) {                    if(current->Left ) {Nodestack.push ( current-Left ); Depthstack.push (Depth-depthgap); } Current= current->Right ; }                 Else{ Current= current->Left ; }                if(!current) Break; }            if(!current)Continue;  while(current) {Ret.push_back ( current-val); Depth++; if(current->Right ) {                    if(current->Left ) {Nodestack.push ( current-Left );                    Depthstack.push (depth); } Current= current->Right ; }                 Else{ Current= current->Left ; }            }        }        returnret; }};

199. Binary Tree Right Side View (Tree, Stack)