剑指offer---按之字形顺序打印二叉树

题目：按之字形顺序打印二叉树

要求：请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

/*
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) {
        
    }
    
};

解题代码：

class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        vector<vector<int> > res;
        vector<int> subRes;
        if(pRoot == nullptr)
            return res;

        queue<TreeNode*> q;
        q.push(pRoot);
        TreeNode *temp = pRoot;
        int currentLevel= 1;
        int nextLevel = 0;
        int flag = 1;
        while(!q.empty()){
            temp = q.front();
            q.pop();
            subRes.push_back(temp->val);
            if(temp->left){
                q.push(temp->left);
                nextLevel++;
            }
            if(temp->right){
                q.push(temp->right);
                nextLevel++;
            }
            currentLevel--;
            if(currentLevel == 0){
                if(flag == -1)
                    reverse(subRes.begin(), subRes.end());
                res.push_back(subRes);
                subRes.clear();
                currentLevel = nextLevel;
                nextLevel = 0;
                flag = -1 * flag;
            }
        }
        return res;
    }
};