剑指offer- 把二叉树打印成多行

题目描述
从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

层次打印二叉树

vector<int> PrintFromTopToBottom(TreeNode* root) 
{
    queue<TreeNode*> q;
    vector<int> v;
    if(root==nullptr)return v;
    q.push(root);
    while(!q.empty())
    {
        root = q.front(); //记录队头
        if(root->left)q.push(root->left);//如果有子节点则，入队
        if(root->right)q.push(root->right);
        v.push_back(root->val);//队头的值打印
        q.pop();
    }
    return v;
}

分行层次打印

 vector<vector<int>> Print(TreeNode* root) 
{
    queue<TreeNode*> q;
    vector<vector<int> > V;
    if(root==nullptr)return V;
    q.push(root);
    while(!q.empty())
    {
        vector<int> tmp;//存一行的节点
        int n = q.size();
        while(n--)
        {
            root = q.front();
            tmp.push_back(root->val);
            if(root->left)q.push(root->left);
            if(root->right)q.push(root->right);
             q.pop();
        }
        V.push_back(tmp);
    }
    return V;
}