题解 | #求二叉树的层序遍历#

class Solution {
public:
   		vector<vector<int> > levelOrder1(TreeNode* root) {
        vector<vector<int>> res;
        if (root == nullptr)
            return res;
        queue<TreeNode*> q;
        q.push(root);
        TreeNode* cur;
        while (!q.empty()) {
            vector<int> ret;
            int n = q.size();

            for (int i = 0; i < n; ++i) {
                cur = q.front();
                q.pop();
                ret.push_back(cur->val);
                if (cur->left)
                    q.push(cur->left);
                if (cur->right)
                    q.push(cur->right);
            }
            res.push_back(ret);
        }
        return res;
    }
    void levelOrder_(TreeNode* root,int n,vector<vector<int>>& res)
    {
        if(root==nullptr)
            return;
        else
         {
            if(res.size()<n)
                res.push_back(vector<int>{});
            res[n-1].push_back(root->val);
         }
        levelOrder_(root->left, n+1, res);
        levelOrder_(root->right, n+1, res);
    }
    vector<vector<int> > levelOrder(TreeNode* root) {
        vector<vector<int>> res;
        levelOrder_(root,1,res);
        return res;
   }
};