//使用双向队列，用单向的队列就可以/*
struct TreeNode {int val;struct TreeNode *left;struct TreeNode *right;TreeNode(int x) :val(x), left(NULL), right(NULL) {}
};*/
class Solution {
public:vector<int> PrintFromTopToBottom(TreeNode* root) {vector<int> result;if(root==nullptr)return result;deque<TreeNode*> saveNodes;saveNodes.push_back(root);//error: while(saveNodes)  saveNodes没有对应的bool值while(!saveNodes.empty()){  //队列非空的时候   TreeNode* currNode = saveNodes.front();saveNodes.pop_front();result.push_back(currNode->val);if(currNode->left) //右子树非空，追加在队列的后面saveNodes.push_back(currNode->left);if(currNode->right) //左子树非空，追加在队列的后面saveNodes.push_back(currNode->right);}return result;}
};

//单向队列class Solution {
public:vector<int> PrintFromTopToBottom(TreeNode* root) {vector<int> result;if(root==nullptr)return result;queue<TreeNode*> saveNodes;saveNodes.push(root);//error: while(saveNodes)  saveNodes没有对应的bool值while(!saveNodes.empty()){  //队列非空的时候   TreeNode* currNode = saveNodes.front();saveNodes.pop();result.push_back(currNode->val);if(currNode->left) //右子树非空，追加在队列的后面saveNodes.push(currNode->left);if(currNode->right) //左子树非空，追加在队列的后面saveNodes.push(currNode->right);}return result;}
};　　

class Solution {
public:vector<vector<int> > Print(TreeNode* pRoot) {vector<vector<int> > result;if(pRoot==nullptr)return result;vector<int> row;queue<TreeNode*> treeNodes;treeNodes.push(pRoot);int toBePrint = 1; //初始化为1，根节点int nextLevel = 0;while(!treeNodes.empty()){TreeNode* pNode = treeNodes.front();treeNodes.pop();row.push_back(pNode->val); toBePrint--;if(pNode->left){treeNodes.push(pNode->left);nextLevel++;}if(pNode->right){treeNodes.push(pNode->right);nextLevel++;}if(toBePrint==0){result.push_back(row);//删除行！！vector<int>().swap(row);toBePrint = nextLevel;nextLevel = 0;}}return result;}
};　

class Solution {
public:vector<vector<int> > Print(TreeNode* pRoot) {vector<vector<int> > result;if(pRoot==nullptr)return result;int row = 0;queue<TreeNode*> treeNodes;treeNodes.push(pRoot);int toBePrint = 1; //初始化为1，根节点int nextLevel = 0;while(!treeNodes.empty()){TreeNode* pNode = treeNodes.front();treeNodes.pop();(result[row]).push_back(pNode->val); //error: 不能这样使用 result[row].push_backtoBePrint--;if(pNode->left){treeNodes.push(pNode->left);nextLevel++;}if(pNode->right){treeNodes.push(pNode->right);nextLevel++;}if(toBePrint==0){row++;toBePrint = nextLevel;nextLevel = 0;}}return result;}
};

class Solution {
public:vector<vector<int> > Print(TreeNode* pRoot) {vector<vector<int> > result;if(pRoot == NULL) return result;queue<TreeNode*> q;q.push(pRoot);while(!q.empty()){ //每一个while循环打印一行int index = 0;  //用于遍历每行元素int numNodes = q.size();  //当前行的元素数==队列里的元素数vector<int> row; //用于存储每行的元素。while(index++ < numNodes){TreeNode *currNode = q.front();q.pop();row.push_back(currNode->val);if(currNode->left) q.push(currNode->left);if(currNode->right) q.push(currNode->right);}result.push_back(row);}return result;}
};

class Solution {
public:vector<vector<int> > Print(TreeNode* pRoot) {vector<vector<int> > result;if(pRoot==nullptr)return result;queue<TreeNode*> treeNodes;treeNodes.push(pRoot);int count=1; //记录单行还是双行while(!treeNodes.empty()){vector<int> row; //用于存每行的元素 //每次循环都会被清零int numNodesInRow = treeNodes.size();  //每行元素的个数while(numNodesInRow--){TreeNode* curr = treeNodes.front(); //访问treeNodes.pop(); //删除row.push_back(curr->val);  //读取当前节点的元素if(curr->left)treeNodes.push(curr->left);if(curr->right)treeNodes.push(curr->right);}if((count & 0x1)==1){//第几行result.push_back(row);}else{vector<int> inverseRow(row.rbegin(),row.rend());result.push_back(inverseRow);}count++;}return result;}};

//实现1class Solution {
public:vector<vector<int> > Print(TreeNode* pRoot) {vector<vector<int> > result;if(pRoot==nullptr)return result;//使用两个栈存储stack<TreeNode*> oddRow,evenRow;vector<int> row; //存储每行的遍历元素int numRow = 1;evenRow.push(pRoot);while(oddRow.size() || evenRow.size()){//两个栈有一个非空时，进入循环if((numRow & 0x1)==1){ //奇数行 从左到右 且先遍历左子树while(evenRow.size()){TreeNode* pNode = evenRow.top();evenRow.pop();row.push_back(pNode->val);if(pNode->left)oddRow.push(pNode->left);if(pNode->right)oddRow.push(pNode->right);}}else{ //偶数行 从右到左 且先遍历右子树while(oddRow.size()){TreeNode* pNode = oddRow.top();oddRow.pop();row.push_back(pNode->val);if(pNode->right)evenRow.push(pNode->right);if(pNode->left)evenRow.push(pNode->left);}}//遍历完一行result.push_back(row);vector<int>().swap(row);  //将row清空，便于下一行的存储numRow++;}return result;}};

//实现2
class Solution {
public:vector<vector<int> > Print(TreeNode* pRoot) {vector<vector<int> > result;if(pRoot==nullptr)return result;//使用两个栈存储stack<TreeNode*> levels[2];vector<int> row; //存储每行的遍历元素int current = 0;int next = 1;levels[current].push(pRoot);  //while(levels[0].size() || levels[1].size() ){TreeNode* pNode = levels[current].top(); //读取当前节点levels[current].pop();  //删除读取过的节点row.push_back(pNode->val);if(current==0){ //奇数行，先存左子树if(pNode->left)levels[next].push(pNode->left);if(pNode->right)levels[next].push(pNode->right);}else{ //偶数行，先存右子树if(pNode->right)levels[next].push(pNode->right);if(pNode->left)levels[next].push(pNode->left);}if(levels[current].empty()){ //当前栈为空时，换栈result.push_back(row);vector<int> ().swap(row); //清空rowcurrent = 1 - current;  //交换栈next = 1 - next;}}return result;}};