二叉树的锯齿形层次遍历

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）

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 {
    /**
     * @param root: The root of binary tree.
     * @return: A list of lists of integer include 
     *          the zigzag level order traversal of its nodes' values 
     */
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode *root) {
        // write your code here
        vector<vector<int>>res;
        if(root==NULL) return res;
        queue<TreeNode*>q;
        q.push(root);
        int line=0;
        while(!q.empty()){
            int size=q.size();
            vector<int>oneLevel;
            for(int i=0;i<size;i++){
                TreeNode*tmp=q.front();q.pop();
                oneLevel.push_back(tmp->val);
                if(tmp->left) q.push(tmp->left);
                if(tmp->right) q.push(tmp->right);
            }
            if(line%2==0) res.push_back(oneLevel);
            else{
                reverse(oneLevel.begin(),oneLevel.end());
                res.push_back(oneLevel);
            }
            line++;
        }
        return res;
    }
};