// bfs 代码 class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> ret;
        queue<pair<TreeNode*, int>> que;
        if(root) que.push({root, 1});
        while(!que.empty()) {
            auto front = que.front(); que.pop();
            if(front.second == ret.size()) {
                ret.back() = front.First -> val;
            }
            else {
                ret.push_back(front.first -> val);
            }
            if(front.first -> left) {
                que.push({front.first -> left, front.second + 1});
            }
            if(front.first -> right) {
                que.push({front.first -> right, front.second + 1});
            }
        }
        return ret;
    }
};