[LeetCode] Binary Tree Zigzag Level Order Traversal

标签：c++   leetcode   binary tree   

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.

解题思路：

可以先获得二叉树的高度，分配vector的大小，然后通过先序遍历，插入对应的层中。根据深度的奇偶来选择插在前面还是插在后面。

/**
 * 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) {
        int h = getHeight(root);
        vector<vector<int>> result(h, vector<int>());
        preOrder(root, 0, result);
        return result;
    }
    
    void preOrder(TreeNode* root, int h, vector<vector<int>>& result){
        if(root==NULL){
            return;
        }
        if(h%2==0){
            result[h].push_back(root->val);
        }else{
            result[h].insert(result[h].begin(), root->val);
        }
        preOrder(root->left, h+1, result);
        preOrder(root->right, h+1, result);
    }
    
    int getHeight(TreeNode* root){
        if(root == NULL){
            return 0;
        }
        return 1 + max(getHeight(root->left), getHeight(root->right));
    }
};

[LeetCode] Binary Tree Zigzag Level Order Traversal

标签：c++   leetcode   binary tree   

原文地址：http://blog.csdn.net/kangrydotnet/article/details/47337645