leetcode_question_103 Binary Tree Zigzag Level Order Traversal

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3   / \  9  20    /  \   15   7

return its zigzag level order traversal as:

[  [3],  [20,9],  [15,7]]

BFS:

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector<vector<int>> matrix;    if(root == NULL) return matrix;vector<int> tmp;tmp.push_back(root->val);matrix.push_back(tmp);vector<TreeNode*> path;path.push_back(root);int count = 1;bool lefttoright = false;while(!path.empty()){if(path[0]->left) path.push_back(path[0]->left);if(path[0]->right) path.push_back(path[0]->right);path.erase(path.begin());count--;if(count == 0 && path.size()){vector<int> tmp;if(lefttoright){vector<TreeNode*>::iterator it = path.begin();for(; it != path.end(); ++it)tmp.push_back((*it)->val);lefttoright = false;}else{vector<TreeNode*>::iterator it = path.end();for(--it;it>=path.begin();--it)tmp.push_back((*it)->val);lefttoright = true;}matrix.push_back(tmp);count = path.size();}}return matrix;    }};