文章作者：Tyan 部落格：noahsnail.com  |  CSDN  |  簡書

1. Description

2. Solution

/**
 * 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>> result;
        zigzagTraverse(result, root, 0);
        for(int i = 0; i < result.size(); i++) {
            if(i % 2 == 1) {
                reverse(result[i].begin(), result[i].end());
            }
        }
 

        return result;
    }
    
private:
    void zigzagTraverse(vector<vector<int>>& result, TreeNode* root, int depth) {
        if(!root) {
            return;
        }
        depth++;
        if(depth > result.size()) {
            vector<int> values;
            result.
 
emplace_back(values);
        }
        result[depth - 1].push_back(root->val);
        zigzagTraverse(result, root->left, depth);
        zigzagTraverse(result, root->right, depth);
    }
};

Reference