从上到下打印二叉树(II)
与I类似,要按层打印,所以每次先获取队列的长度,这个长度即为该层元素的个数,然后将其保存到数组中,依次将其左右节点压入队列;
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int>> levelOrder(TreeNode* root) {
vector<vector<int>> res;
if(!root) return res;
queue<TreeNode*> q;
q.push(root);
while(!q.empty())
{
vector<int> v;
int len = q.size();
while(len--)
{
TreeNode* tmp = q.front();
v.push_back(tmp->val);
q.pop();
//顺序不能颠倒
if(tmp->left) q.push(tmp->left);
if(tmp->right) q.push(tmp->right);
}
res.push_back(v);
}
return res;
}
};