简单

题目描述

class Solution {
public:
    vector<vector<int>> printFromTopToBottom(TreeNode* root) {
        if (!root) return {};

        vector<vector<int>> vec {};
        queue<TreeNode*> q {{root}};

        while(!q.empty()) {
            auto size = q.size();
            vector<int> vLevel(size);

            for (size_t i = 0; i < size; i++) {
                auto node = q.front(); q.pop();
                vLevel[i] = node->val;
                if (node->left) q.push(node->left);
                if (node->right) q.push(node->right);
            }
            vec.emplace_back(move(vLevel));
        }
        return vec;
    }
};