lintcode-二叉树的锯齿形层次遍历-71

给出一棵二叉树，返回其节点值的锯齿形层次遍历（先从左往右，下一层再从右往左，层与层之间交替进行） 

样例

给出一棵二叉树 {3,9,20,#,#,15,7},

    3
   / \
  9  20
    /  \
   15   7

返回其锯齿形的层次遍历为：

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

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
 
class Solution {
public:
    vector> zigzagLevelOrder(TreeNode *root) {
        vector > vec;
        if(!root)
            return vec;
        bool open=false;    
        queue que;
        que.push(root);
        while(!que.empty()){
            int count=que.size();
            vector base;
            while(count--){
                TreeNode *tmp=que.front();
                que.pop();
                base.push_back(tmp->val);
                if(tmp->left)
                    que.push(tmp->left);
                if(tmp->right)
                    que.push(tmp->right);
            }
            if(open)
                reverse(base.begin(),base.end());
            open=!open;
            vec.push_back(base);    
        }
        return vec;    
    }
};