For populating test cases for those LeetCode problems with binary trees

populate_tree.cpp

#include <type_traits>
#include <concepts>
#include <vector>
#include <optional>
#include <iostream>

template <typename T>
struct TreeNodeGeneric
{
	T val;
	TreeNodeGeneric *left;
	TreeNodeGeneric *right;
	TreeNodeGeneric() requires std::integral<T> : val(0), left(nullptr), right(nullptr) {}
	TreeNodeGeneric(T val) : val(val), left(nullptr), right(nullptr) {}
	TreeNodeGeneric(T val, TreeNodeGeneric *left, TreeNodeGeneric *right) : val(val), left(left), right(right) {}
};

template <typename T>
void Populate(const std::vector<std::optional<T>> &values,std::vector<TreeNodeGeneric<T>*> level,int index)
{
	if (index == 0) level.at(0)->val=*values.at(index);
	std::vector<TreeNodeGeneric<T>*> nextLevel;

	try
	{
		for (TreeNodeGeneric<T> *node : level)
		{
			node->left=values.at(++index) ? new TreeNodeGeneric<T>(*values.at(index)) : nullptr;
			nextLevel.push_back(node->left);
			node->right=values.at(++index) ? new TreeNodeGeneric<T>(*values.at(index)) : nullptr;
			nextLevel.push_back(node->right);
		}
	}

	catch (const std::out_of_range &exception) {}

	if (index < values.size()-1) Populate(values,nextLevel,index);
}

template <typename T>
void Populate(const std::vector<std::optional<T>> &values,TreeNodeGeneric<T>* root)
{
	Populate(values,{root},0);
}

using TreeNode=TreeNodeGeneric<int>;