题目:从上到下打印二叉树 II
从上到下按层打印二叉树,同一层的节点按从左到右的顺序打印,每一层打印到一行。
例如:
给定二叉树: [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回其层次遍历结果:
[
[3],
[9,20],
[15,7]
]
提示:节点总数 <= 1000
解题:利用二维向量
/**
* 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==NULL)return res;
queue<TreeNode*>q;
q.push(root);
while(!q.empty()){
vector<int> r;
int l=q.size();
for(int i=0;i<l;i++){ //当前层节点都在队列中,依次取出
TreeNode* t=q.front();
q.pop();
if(t == nullptr) continue;
r.push_back(t->val);
if(t->left)q.push(t->left);
if(t->right)q.push(t->right);
}
res.push_back(r);
}
return res;
}
};