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class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int>result;
        if(!root)return result;
        
        queue<TreeNode*>q;
        q.push(root);
        while(!q.empty()){
            int size=q.size();
            TreeNode*lastnode=nullptr;
            for(int i=0;i<size;++i){
            TreeNode*node=q.front();
            q.pop();
            lastnode=node;
            if(node->left)q.push(node->left);
            if(node->right)q.push(node->right);
        }
        result.push_back(lastnode->val);
        }
        return result;
    }
};

https://leetcode.cn/problems/binary-tree-right-side-view/description/