lc 二叉树的锯齿形层次遍历

链接：https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/

代码：

/**
 * 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) {
        if(root == nullptr) return {};
        vector<vector<int>> res;
        vector<TreeNode*> v;
        v.push_back(root);
        int ltor = 1;
        while(1) {
            int vn = v.size();
            if(ltor) {
                // cout << vn << endl;
                vector<int> temp_res;
                for(int i = 0; i < vn; i++) {
                    temp_res.push_back(v[i]->val);
                }
                res.push_back(temp_res);
            }
            else {
                vector<int> temp_res;
                for(int i = vn-1; i >= 0; i--) {
                    temp_res.push_back(v[i]->val);
                }
                res.push_back(temp_res);
            }
            vector<TreeNode*> temp_v;
            for(int i = 0; i < vn; i++) {
                if(v[i]->left) temp_v.push_back(v[i]->left);
                if(v[i]->right) temp_v.push_back(v[i]->right);
            }
            int temp_len = temp_v.size();
            if(!temp_len) break;
            
            v.clear();
            for(int i = 0; i < temp_len; i++) {
                v.push_back(temp_v[i]);
            }
            
            ltor = !ltor;
        }
        return res;
    }
};

思路：层序遍历即可