IMWeb提升营Day4 | 训练题22：从上往下打印二叉树

题目描述

思路

/*
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};*/
/*
* 思路：BFS，用一个队列，每次遍历一次队列，把队列的下一层节点存到队列里
*/
class Solution {
public:
vector<int> PrintFromTopToBottom(TreeNode* root) {
vector<int> result;
if(root == NULL) return result;
queue<TreeNode*> q;
q.push(root);
while(!q.empty()){
int length = q.size();
for(int i = 0; i < length; i++){
result.push_back(q.front()->val);
if(q.front()->left != NULL) q.push(q.front()->left);
if(q.front()->right != NULL) q.push(q.front()->right);
q.pop();
}
}
return result;
}
};