Lua implementation of BestSum function using memoization - dynamic

Question

I am trying to translate the below javascript "bestSum" memoization function into lua:
const bestSum = (targetSum,numbers,memo ={}) => {
if(targetSum in memo) return memo[targetSum];
if(targetSum === 0 ) return [];
if(targetSum <0)return null;
let shortestCombination = null;
for (let num of numbers) {
const remainder = targetSum - num;
const remainderCombination = bestSum(remainder,numbers,memo);
if (remainderCombination !==null) {
const combination = [...remainderCombination, num];
if (shortestCombination === null || combination.length < shortestCombination.length)
{
shortestCombination = combination;
}
}
}
memo [targetSum] = shortestCombination;
return shortestCombination;
}
sample test cases with correct results:
console.log(bestSum(7,[5,3,4,7])); //[7]
console.log(bestSum(8,[2,3,5])); //[3,5]
console.log(bestSum(8,[1,4,5])); //[4,4]
console.log(bestSum(100,[1,2,5,25])); //[25,25,25,25]
I translated the above javascript into lua as the following:
local function BestSum(target_sum,numbers,memo)
if memo[target_sum] ~= nil then return memo[target_sum] end
if target_sum == 0 then return {} end
if target_sum < 0 then return nil end
local shortest_combination = nil
for i, num in ipairs (numbers) do
local remainder = target_sum - num
local remainder_combination = BestSum(remainder,numbers, memo)
if remainder_combination ~= nil then
local combination = remainder_combination
table.insert(combination,num )
if (shortest_combination == nil) or (#combination < #shortest_combination )then
shortest_combination = combination
end
end
end
memo[target_sum] = shortest_combination;
return shortest_combination;
end
but don't get the desired results for the two last cases...... instead get incorrect results:
BestSum(8,{1,4,5},{})==>{"4","1","4"}
BestSum(150,{5,25},{})==>
{"25","5","5","5","5","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25","5","25"}
The results are not even correct let alone being "best" case??
Can anyone spot where I'm going wrong?
Much appreciated

Answer 1

The problem is with this part of the translation:
local combination = remainder_combination
table.insert(combination, num)
Tables are pass by reference, so this isn't creating a new table, it's just assigning the variable combination to the same table. Modifying combination is just adding more data to remainder_combination.
The JavaScript version is taking care to create a new array, and fills it with the contents of the remainderCombination array (using '...', the spread operator):
const combination = [...remainderCombination, num];
This is the most accurate Lua translation:
local combination = {unpack(remainder_combination)}
table.insert(combination, num)
(Edit: For Lua 5.2+ it's table.unpack)