Binary Tree Zigzag Level Order Traversal

Binary Tree Zigzag Level Order Traversal

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]]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

二叉树的层次遍历

 vector<vector<int> > zigzagLevelOrder(TreeNode *root) {        vector<vector<int>> result;        traverse(root,1,result,true);        return result;    }        void traverse(TreeNode* root,size_t level,vector<vector<int>> &result,bool left_to_right)    {        if(!root) return;                if(level>result.size())        result.push_back(vector<int>());                if(left_to_right)            result[level-1].push_back(root->val);        else            result[level-1].insert(result[level-1].begin(),root->val);                    traverse(root->left,level+1,result,!left_to_right);        traverse(root->right,level+1,result,!left_to_right);    }