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47_binary-tree-level-order-traversal.cpp
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47_binary-tree-level-order-traversal.cpp
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// DATE: 07-Aug-2023
/* PROGRAM: 47_Tree - Binary Tree Level Order Traversal
https://leetcode.com/problems/binary-tree-level-order-traversal/
Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from
left to right, level by level).
Example 1:
Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]
Example 2:
Input: root = [1]
Output: [[1]]
Example 3:
Input: root = []
Output: []
*/
// @ankitsamaddar @Aug_2023
#include <iostream>
#include <queue>
#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) {
if (!root) {
return {};
}
vector<vector<int>> ans;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
int qLen = q.size();
vector<int> curLevel;
for (int i = 0; i < qLen; i++) {
TreeNode* node = q.front();
q.pop();
if (node) {
curLevel.push_back(node->val);
q.push(node->left);
q.push(node->right);
}
}
if (!curLevel.empty()) {
ans.push_back(curLevel);
}
}
return ans;
}
};
vector<int> parseInput(string input) {
vector<int> result;
int num = 0;
bool negative = false;
for (char c : input) {
if (isdigit(c)) {
num = num * 10 + (c - '0');
} else if (c == 'n') {
num = INT_MAX;
} else if (c == '-') {
negative = true;
} else if (c == ',' || c == ']') {
result.push_back(negative ? -num : num);
num = 0;
negative = false;
}
}
return result;
}
TreeNode* createTree(vector<int>& nums, int i) {
if (i >= nums.size() || nums[i] == INT_MAX) {
return NULL;
}
TreeNode* root = new TreeNode(nums[i]);
root->left = createTree(nums, 2 * i + 1);
root->right = createTree(nums, 2 * i + 2);
return root;
}
string formatOutput(vector<vector<int>>& output) {
string result = "[";
for (auto& level : output) {
result += "[";
for (int i = 0; i < level.size(); i++) {
result += to_string(level[i]);
if (i < level.size() - 1) {
result += ",";
}
}
result += "]";
}
result += "]";
return result;
}
int main() {
string input = "[3,9,20,null,null,15,7]";
vector<int> nums = parseInput(input);
TreeNode* root = createTree(nums, 0);
Solution sol;
vector<vector<int>> output = sol.levelOrder(root);
string formattedOutput = formatOutput(output);
cout << formattedOutput << endl; // expected output: [[3],[9,20],[15,7]]
return 0;
}