103.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
#include <bits/stdc++.h>
#include <gtest/gtest.h>
using namespace std;
struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}

    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}

    TreeNode(int x, TreeNode *left, TreeNode *right)
        : val(x), left(left), right(right)
    {
    }
};
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode *root)
    {
        vector<vector<int>> result;
        if (!root) {
            return result;
        }
        queue<TreeNode *> q;
        q.push(root);
        bool flag = true;
        while (!q.empty()) {
            int size = q.size();
            vector<int> level;
            for (int i = 0; i < size; i++) {
                TreeNode *node = q.front();
                q.pop();
                level.push_back(node->val);
                if (node->left) {
                    q.push(node->left);
                }
                if (node->right) {
                    q.push(node->right);
                }
            }
            if (flag) {
                result.push_back(level);
            }
            else {
                reverse(level.begin(), level.end());
                result.push_back(level);
            }
            flag = !flag;
        }
        return result;
    }
};