剑指offer---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：

 1 class Solution {
 2 public:
 3     vector<vector<int> > Print(TreeNode* pRoot) {
 4         vector<vector<int> > res;
 5         vector<int> subRes;
 6         if(pRoot == nullptr)
 7             return res;
 8 
 9         queue<TreeNode*> q;
10         q.push(pRoot);
11         TreeNode *temp = pRoot;
12         int currentLevel= 1;
13         int nextLevel = 0;
14         int flag = 1;
15         while(!q.empty()){
16             temp = q.front();
17             q.pop();
18             subRes.push_back(temp->val);
19             if(temp->left){
20                 q.push(temp->left);
21                 nextLevel++;
22             }
23             if(temp->right){
24                 q.push(temp->right);
25                 nextLevel++;
26             }
27             currentLevel--;
28             if(currentLevel == 0){
29                 if(flag == -1)
30                     reverse(subRes.begin(), subRes.end());
31                 res.push_back(subRes);
32                 subRes.clear();
33                 currentLevel = nextLevel;
34                 nextLevel = 0;
35                 flag = -1 * flag;
36             }
37         }
38         return res;
39     }
40 };