07
08/2015
[LeetCode] 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] ]
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));
}
};
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