102.二叉树的层序遍历.cpp

/*
 * @lc app=leetcode.cn id=102 lang=cpp
 *
 * [102] 二叉树的层序遍历
 */
#include<iostream>
#include <vector>
#include <queue>
using namespace std;
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
// @lc code=start
/**
 * 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>> levelOrder(TreeNode* root) {
        if (root == nullptr)
            return {};
        vector<vector<int>> res;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            int levelSize = q.size();
            res.push_back({});
            for (int i = 0; i < levelSize; i++) {
                auto head = q.front();
                q.pop();
                res.back().push_back(head->val);
                if (head->left != nullptr)
                    q.push(head->left);
                if (head->right != nullptr)
                    q.push(head->right);
            }
        }
        return res;
    }
};
// @lc code=end