199. Binary Tree Right Side View

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].

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ //解法一，层序遍历class Solution {public:    vector<int> rightSideView(TreeNode* root) {        vector<int> result;        deque<TreeNode*> q;        if(!root) return result;        q.push_back(root);        int count = 0;        int to_be_print = 1;        while(q.size()){            TreeNode* temp = q.front();            q.pop_front();            to_be_print--;            if(temp->left){                q.push_back(temp->left);                count++;            }            if(temp->right){                q.push_back(temp->right);                count++;            }            if(to_be_print == 0) {                result.push_back(temp->val);                to_be_print = count;                count = 0;            }        }        return result;    }};//解法二，递归class Solution {public:    void helper(TreeNode* root,int level,vector<int>& result) {        if(!root) return;        if(result.size() < level) result.push_back(root->val);        if(root->right) helper(root->right,level+1,result);        if(root->left) helper(root->left,level+1,result);    }    vector<int> rightSideView(TreeNode* root) {        vector<int> result;        helper(root,1,result);        return result;    }};