练习：之字形打印二叉树

1、我的代码1：

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        vector<vector<int>> res;
        if(!pRoot) return res;
        vector<TreeNode*> v1, v2;
        v1.push_back(pRoot);
        int k = 1;
        while(!v1.empty()) {
            if(k++ % 2 == 1) {
                for(int i = v1.size()-1;i >= 0;i--) {
                    if(v1[i]->right) v2.push_back(v1[i]->right);
                    if(v1[i]->left) v2.push_back(v1[i]->left);
                }
            } else {
                for(int i = v1.size()-1;i >= 0;i--) {
                    if(v1[i]->left) v2.push_back(v1[i]->left);
                    if(v1[i]->right) v2.push_back(v1[i]->right);
                }
            }
            vector<int> vtmp;
            for(int i = 0;i < v1.size();i++) {
                vtmp.push_back(v1[i]->val);
            }
            res.push_back(vtmp);
            v1.swap(v2);
            v2.clear();
        }
        return res;
    }

};