C++-- 二叉树的层序遍历

题目要求：

题目来源：力扣

class Solution {
public:
    vector> levelOrder(TreeNode* root) {
        if(root == nullptr)
        {
            return vector> ();
        }
        queue q;
        int levelsize = 1;
        q.push(root);
        vector> vv;
        while(!q.empty())
        {
            vector v;
            for(int i = 0;i < levelsize;i++)
            {
                TreeNode* front = q.front();
                q.pop();
                v.push_back(front->val);
                if(front->left)
                    q.push(front->left);
                if(front->right)
                    q.push(front->right);
            }
            vv.push_back(v);
            levelsize = q.size();
        }
        return vv;
    }
};