每天一道LeetCode-----从右向左观察一棵二叉树，返回能看到的元素

Binary Tree Right Side View

/**
* 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> views;
scan(root, 0, views);
return views;
}
private:
void scan(TreeNode* root, int h, vector<int>& views)
{
if(!root)   return;
if(h >= views.size())
views.emplace_back(root->val);
/* 先遍历右侧，这样就可以先选择右边的元素 */
scan(root->right, h + 1, views);
scan(root->left, h + 1, views);
}
};