70_leetcode_Binary Tree Zigzag level order traversal

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于 2014-06-20 10:56:27 发布

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分类专栏：算法编程 leetcode 文章标签： leetcode 算法编程语言面试

本文链接：https://blog.youkuaiyun.com/ezzffzz/article/details/32702069

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本博客介绍了一种二叉树的zigzag层次遍历算法，通过使用队列和标志位实现从左到右和从右到左交替遍历各层节点的值。

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},

return its zigzag level order traversal as:

[
  [3],
  [20,9],
  [15,7]
]

    vector<vector<int> > zigzagLevelOrder(TreeNode *root)
    {
        vector<vector<int > > result;
        if(root == NULL)
        {
            return result;
        }
        
        vector<int> temp;
        bool flag = true;
        deque<TreeNode* > myDeque;
        myDeque.push_back(root);
        myDeque.push_back(NULL);
        
        while(!myDeque.empty())
        {
            TreeNode* tempNode = myDeque.front();
            myDeque.pop_front();
            
            if(tempNode)
            {
                temp.push_back(tempNode->val);
                if(tempNode->left)
                {
                    myDeque.push_back(tempNode->left);
                }
                if(tempNode->right)
                {
                    myDeque.push_back(tempNode->right);
                }
            }
            else
            {
                if(!myDeque.empty())
                {
                    myDeque.push_back(NULL);
                }
                
                if(flag)
                {
                    result.push_back(temp);
                    flag = false;
                }
                else
                {
                    int start = 0;
                    int end = (int)temp.size() - 1;
                    while(start < end)
                    {
                        swap(temp[start++], temp[end--]);
                    }
                    result.push_back(temp);
                    flag = true;
                }
                temp.clear();
            }
        }
        
        
        
        return result;
    }