/*
题目:
按层自上向下打印二叉树。
*/
/*
思路:
使用队列,将节点压入队列中,再弹出来,压入其左右子节点,循环,直到栈为空。
*/
#include<iostream>
#include<string.h>
#include<algorithm>
#include<cmath>
#include<stdio.h>
#include<vector>
#include<stack>
#include<queue>using namespace std;struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};vector<int> PrintFromTopToBottom(TreeNode* root){
vector<int> sequence;
if(root == nullptr) return sequence; deque<TreeNode*> myQueue;
myQueue.push_back(root);
TreeNode *temp; while(!myQueue.empty()){
temp = myQueue.front();
myQueue.pop_front();
sequence.push_back(temp->val);
if(temp->left != nullptr){
myQueue.push_back(temp->left);
}
if(temp->right != nullptr){
myQueue.push_back(temp->right);
}
}
return sequence;
}int main(){
TreeNode* node1 = new TreeNode(1);
TreeNode* node2 = new TreeNode(2);
TreeNode* node3 = new TreeNode(3);
node1->left = node2;
node2->right = node3;
vector<int> m = PrintFromTopToBottom(node1);
for(int i = 0; i < m.size(); i++){
cout<<m[i]<<" ";
}
}