Leetcode Note: Binary Tree Zigzag Level Order Traversal

Leetcode Note: Binary Tree Zigzag Level Order Traversal

I. Description

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 ).
For example: Given binary tree, 20,

   3  /   9 20    /    15  7

Ii. Question Analysis

BFS. Here, a bool record is used to read data from left to right or from right to left. After each layer traversal ends, it is flipped.

Iii. Sample Code

#include 
  
   #include 
   
    using namespace std;struct TreeNode{    int val;    TreeNode *left;    TreeNode *right;    TreeNode(int x) :val(x), left(NULL), right(NULL){}};class Solution{public:    vector
    
      > zigzagLevelOrder(TreeNode *root)    {        vector
     
       > result;        Traverse(root, 1, result, true);        return result;    }private:    void Traverse(TreeNode *root, size_t level, vector
      
        > & result, bool leftToRight) { if (root == NULL) return; if (level > result.size()) result.push_back(vector
       
        ()); if (leftToRight) result[level - 1].push_back(root->val); else result[level - 1].insert(result[level - 1].begin(), root->val); Traverse(root->left, level + 1, result, !leftToRight); Traverse(root->right, level + 1, result, !leftToRight); }};
       
      
     
    
   
  

Iv. Summary

It is a little more difficult than Binary Tree Level Order Traversal and Binary Tree Level Order Traversal II. Pay attention to more details.