leetCode(23):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]]

又是层序遍历！！！

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {        queue<TreeNode*> nodes;    vector< vector<int> > result;    vector<int> tmp;    if(NULL==root)    return result;    nodes.push(root);    bool flag=false;    while(!nodes.empty())    {    int length=nodes.size();    int i=0;    while(i<length)    {    TreeNode* tmpNode=nodes.front();    tmp.push_back(tmpNode->val);    if(tmpNode->left)    nodes.push(tmpNode->left);    if(tmpNode->right)    nodes.push(tmpNode->right);    nodes.pop();    i++;    }    if(flag)    {    reverse(tmp.begin(),tmp.end());    flag=false;    }    else    {    flag=true;    }    result.push_back(tmp);    tmp.clear();    }    return result;    }};