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]]

BFS,宽度查找法，把同一级别的宽度记下来，访问的同时把下一层弄到队列里面去。常用遍历方法!

class Solution {public:  vector<vector<int>> zigzagLevelOrder(TreeNode* root) {vector<vector<int>> levelOrderStore;if (root==NULL)return levelOrderStore;queue<TreeNode *>q;stack<TreeNode *>rightout;q.push(root);rightout.push(root);int count=1;int level=0;vector<int> tmp(0);int flag=0;//begin  right->left->rightwhile (!q.empty())//q.root{tmp.clear();level=0;for (int i=0;i<count;i++)//level{root=q.front(); //every root.q.pop();if (flag%2==0){tmp.push_back(root->val);}else{tmp.push_back(rightout.top()->val); //every root.rightout.pop();//}if (root->left!=NULL){q.push(root->left);if (flag%2==0){rightout.push(root->left); //}++level;}if (root->right!=NULL){q.push(root->right);if (flag%2==0)rightout.push(root->right);++level;}}count=level;levelOrderStore.push_back(tmp);flag++;}return levelOrderStore;}};