给定一个二叉树,返回其节点值的锯齿形层次遍历。(即先从左往右,再从右往左进行下一层遍历,以此类推,层与层之间交替进行)。
例如:
给定二叉树 [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回锯齿形层次遍历如下:
[
[3],
[20,9],
[15,7]
]
来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal
/** * 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> >a; vector<int>b; void dfs(TreeNode* root,int cen){ if(root!=NULL){ while(cen>=a.size())a.push_back(b); a[cen].push_back(root->val); dfs(root->left,cen+1); dfs(root->right,cen+1); } } vector<vector<int>> zigzagLevelOrder(TreeNode* root) { dfs(root,0); for(int i=0;i<a.size();i++){ if(i%2){ for(int j=0;j<a[i].size()/2;j++){ swap(a[i][j],a[i][a[i].size()-j-1]); } } } return a; } };