Leetcode|BFS每层最后1个节点|199. 二叉树的右视图

class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        if (!root) return {};
        vector<int> res;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            int sz = q.size();
            for (int i = 0; i < sz; i++) {
                auto node = q.front(); q.pop();
                if (node->left) q.push(node->left);
                if (node->right) q.push(node->right);
                // 添加当前层的最后1个节点到解中
                if (i == sz - 1) res.emplace_back(node->val);
            }
        }
        return res;
    }
};