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.

Example:

Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

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


二叉树的右视图

C++：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> res ;
        if (root == NULL)
            return res ;
        queue<TreeNode*> q ;
        q.push(root) ;
        while(!q.empty()){
            int len = q.size() ;
            for(int i = 0 ; i < len ; i++){
                TreeNode* node = q.front() ;
                q.pop() ;
                if (node->left != NULL)
                    q.push(node->left) ;
                if (node->right != NULL)
                    q.push(node->right) ;
                if (i == len-1){
                    res.push_back(node->val) ;
                }
            }
        }
        return res ;
    }
};