Binary Tree Zigzag Level Order Traversal

题目：

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]]

代码如下：

void getleverorder(TreeNode *root,vector<vector<int> > &getnode,int i)
    {
        if(root!=NULL)
        {
            if(i>getnode.size())
            {
                vector<int> tmp;
                tmp.push_back(root->val);
                getnode.push_back(tmp);
            }
            else
            {
                getnode[i-1].push_back(root->val);
            }
            getleverorder(root->left,getnode,i+1);
            getleverorder(root->right,getnode,i+1);
        }
        return;
    }
    void swap(vector<int> &tmp)
    {
        int n=tmp.size()-1,i=0;
        while(i<n)
        {
            int t=tmp[i];
            tmp[i++]=tmp[n];
            tmp[n--]=t;
        }
        return;
    }
    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
        vector<vector<int> > getnode;
        int i=1;
        getleverorder(root,getnode,i);
        for(int i=0;i<getnode.size();i++)
        {
            if(i%2==1)
            {
                swap(getnode[i]);
            }
        }
        return getnode;
    }