题解 | #求二叉树的层序遍历#

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > levelOrder(TreeNode* root) {
        vector<vector<int>> ans;
        vector<int> vec;
        queue<TreeNode*> que;
        if(root==nullptr) return {};
        que.push(root);
        while(!que.empty()){
            int k = que.size();
            while(k--){
                root = que.front();
                que.pop();
                vec.push_back(root->val);
                if(root->left) que.push(root->left);
                if(root->right) que.push(root->right);
            }
            ans.push_back(vec);
            vec.clear();
        }
        return ans;
    }
};