# 15 lines concise and easy understand c++ solution both recursive and iteration version

• Recursive version:

``````class Solution {
public:
vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
vector<vector<int>> res;
dfs(res, root, 0);
for(int i = 0; i < res.size(); i++)
if(i % 2) reverse(res[i].begin(), res[i].end());
return res;
}
void dfs(vector<vector<int>>& res, TreeNode* root, int level){
if(root){
if(res.size() <= level) res.push_back(vector<int> ());
res[level].push_back(root->val);
}else return;
dfs(res, root->left, level + 1);
dfs(res, root->right, level + 1);
}
};
``````

Iterative version:

``````class Solution {
public:
vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
if(!root) return {};
queue<TreeNode*> que;
que.push(root);
vector<vector<int>> res;
bool lefttoright = true;
while(!que.empty()){
int size = que.size();
vector<int> row(size, 0);
for(int i = 0; i < size; i++){
TreeNode* tmp = que.front();
que.pop();
int index = lefttoright ? i : size - i - 1;
row[index] = tmp->val;
if(tmp->left) que.push(tmp->left);
if(tmp->right) que.push(tmp->right);
}
lefttoright = !lefttoright;
res.push_back(row);
}
return res;
}
};``````

Looks like your connection to LeetCode Discuss was lost, please wait while we try to reconnect.