Binary Tree Right Side View

從右向左觀察一棵二叉樹，返回能看到的元素

遍歷一遍即可，只記錄靠右的元素

程式碼如下

/**
 * 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);
        /* 先遍歷右側，這樣就可以先選擇右邊的元素 */
 

        scan(root->right, h + 1, views);
        scan(root->left, h + 1, views);
    }
};