题目描述
从上到下按层打印二叉树,同一层的结点按从左到右的顺序打印,每一层打印到一行。
样例
输入如下图所示二叉树[8, 12, 2, null, null, 6, null, 4, null, null, null]
8
/ \
12 2
/
6
/
4
输出:[[8], [12, 2], [6], [4]]
C++ 代码
/**
* 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>> printFromTopToBottom(TreeNode* root) {
vector<vector<int>> res;
if(!root) return res;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
queue<TreeNode*> q1;
vector<int> v1;
while (!q.empty()) {
q1.push(q.front());
q.pop();
}
while (!q1.empty()) {
TreeNode* t = q1.front();
q1.pop();
v1.push_back(t->val);
if (t->left) q.push(t->left);
if (t->right) q.push(t->right);
}
res.push_back(v1);
}
return res;
}
};