Binary Tree Level Order Traversal.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 <vector>


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>> levelOrder(TreeNode* root)
    {
        vector<vector<int>> res;
        levelorder(root, 0, res);
        return res;
    }
    void levelorder(TreeNode* root, int level, vector<vector<int>> &res)
    {
        if(root == nullptr) return;
        if(res.size() == level) res.push_back({});
        res[level].push_back(root->val);
        if(root->left) levelorder(root->left, level + 1, res);
        if(root->right) levelorder(root->right, level + 1, res);
        
    }
};