JZ32 题解 | #从上往下打印二叉树#

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
#include <deque>
using namespace std;

class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
		vector<int> res;
		if (root == nullptr) {
			return res;
		}
		// 二叉树的层序遍历，借助队列保存每一层节点
		deque<TreeNode*> myDeque;
		myDeque.push_back(root);
		while (!myDeque.empty()) {
		    // 获取队列中的元素长度
			int sz = myDeque.size();
		    // 遍历队列中的每一层节点
			for (int i = 0; i < sz; i++) {
				TreeNode* front = myDeque.front();
				if (front != nullptr) {
					res.push_back(front->val);
				}
				myDeque.pop_front();
				if (front->left != nullptr) {
					myDeque.push_back(front->left);
				}
				if (front->right != nullptr) {
					myDeque.push_back(front->right);
				}
			}
		}
		return res;
    }
};