LeetCode 199. 二叉树的右视图

LeetCode 199. 二叉树的右视图
思路：

中序遍历把每一层的最后一个放进去

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    queue<TreeNode*> q;
    vector<int> res;
    vector<int> rightSideView(TreeNode* root) {
        //中序遍历把每一层的最后一个放进去
        if(!root ) return res;
        if(!root->left && !root->right) return {root->val};
        q.push(root);
        while(q.size()){
            int len = q.size();
            while(len--){
                auto root = q.front();
                q.pop();
                if(root->left) q.push(root->left);
                if(root->right) q.push(root->right);
                if(len == 0) res.push_back(root->val);
            }
        }
        return res;
    }
};