leetcode 103. 二叉树的锯齿形层次遍历(Binary Tree Zigzag Level Order Traversal)
题目描述:
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)。
示例:
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]
]
解法:
/**
* 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;
vector<TreeNode*> cur, nxt;
bool forward = true;
if(root){
cur.push_back(root);
vector<int> lst;
while(!cur.empty()){
lst.clear();
nxt.clear();
for(TreeNode* node : cur){
lst.push_back(node->val);
if(node->left){
nxt.push_back(node->left);
}
if(node->right){
nxt.push_back(node->right);
}
}
if(forward == false){
forward = true;
lst = vector<int>(lst.rbegin(), lst.rend());
}else{
forward = false;
}
res.push_back(lst);
cur = nxt;
}
}
return res;
}
};