Binary Tree Zigzag Level Order Traversal

Binary Tree Zigzag Level Order Traversal

Given binary tree [3,9,20,null,null,15,7],

    3   / \  9  20    /  \   15   7

return its zigzag level order traversal as:

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

先层次遍历，对于特定行后续处理

/** * 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) {    vector< vector<int> >res;    if(root==NULL)return res;    queue<TreeNode*>qu;    qu.push(root);    while(qu.size()>0){    queue<TreeNode*>tmp_node;    vector<int>tmp_res;    while(qu.size()>0){        TreeNode *p=qu.front();        qu.pop();        if(p->left)tmp_node.push(p->left);        if(p->right)tmp_node.push(p->right);        tmp_res.push_back(p->val);    }    qu=tmp_node;    res.push_back(tmp_res);    }    for(int i=1;i<res.size();i+=2)        reverse(res[i].begin(),res[i].end());    return res;    }};