[leetcode]103. Binary Tree Zigzag Level Order Traversal
[leetcode]103. Binary Tree Zigzag Level Order Traversal
Analysis
fighting—— [每天刷题并不难0.0]
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).
Explanation:
Traversing the given binary tree by level, first level:from left to right, second level:from right to left, third level:from left to right…
Implement
/**
* 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;
if(!root)
return res;
queue<TreeNode*> nq;
nq.push(root);
bool left2right = true;
while(!nq.empty()){
int size = nq.size();
vector<int> tmp;
for(int i=0; i<size; i++){
TreeNode* node = nq.front();
nq.pop();
tmp.push_back(node->val);
if(node->left)
nq.push(node->left);
if(node->right)
nq.push(node->right);
}
if(!left2right)
reverse(tmp.begin(), tmp.end());
res.push_back(tmp);
left2right = !left2right;
}
return res;
}
};