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Vincent Agbo
Vincent Agbo

Reputation: 53

How do I multiply two lists in flutter

How do I multiply two distinct lists in flutter. Like example below

List a = [2,3];

List b = [1,4];

List c = [3,5];

how do I obtain

List d = [6,60];

Upvotes: 0

Views: 2050

Answers (3)

Aamir
Aamir

Reputation: 493

Generalized function to do this, where input is a List of a List of integers, where the lengths of each list can be anything.

List<int> productList(List<List<int>> input) {
  // handle some edge cases
  if (input.isEmpty) {
    return [];
  } else if (input.length < 2) {
    return input.first;
  }
  // sort the input so the largest list is first
  input.sort(
    (listA, listB) => listB.length.compareTo(listA.length),
  );
  var product = input.first;
  for (var productIndex = 0; productIndex < product.length; productIndex++) {
    // iterate over the rest of the list, keep multiplying if each list
    // contains a number at productIndex
    for (var inputIndex = 1; inputIndex < input.length; inputIndex++) {
      var numList = input[inputIndex];
      if (numList.length > productIndex) {
        product[productIndex] *= numList[productIndex];
      } else {
        break;
      }
    }
  }
  return product;
}

In your example:

var a = [2,3];
var b = [1,4];
var c = [3,5];
var input = [a, b, c];
print(productList(input));

yields:

[6, 60]

Upvotes: 0

yaguarete
yaguarete

Reputation: 660

if you do not know:

  • amount of lists you receive
  • amount of elements in the lists

You can do something like:

void main() {
  //creating an empty growable list of list
  List<List<int>> listOfLists = List.generate(0, (i) => []);

  //your N List, maybe from api or something
  List<int> a = [2, 3];
  List<int> b = [1, 4];
  List<int> c = [3, 5];

  //adding all list to main one
  listOfLists.addAll([a, b, c]);

  //creating list which will have results
  final results = [];

  //recursive logic
  listOfLists.asMap().forEach((listOfListsIndex, list) {
    if (listOfListsIndex == 0) {
      //adding first values as there's none to multiply
      //you can remove the if statement if you init earlier
      //final results = listOfLists[0];
      //listOfLists.removeAt(0);
      results.addAll(list);
    } else {
      list.asMap().forEach((listIndex, value) {
        if (results.length > listIndex) {
          //case when listOfLists[0] length is minor
          //preventing error
          //List<int> a = [2];
          //List<int> b = [1, 4];
          //List<int> c = [3, 5];
          //List<int> d = [3, 5, 4, 6, 7];
          results[listIndex] = results[listIndex] * value;
        } else {
          results.add(value);
        }
      });
    }
  });

  print(results);
  //[6, 60]
}

Upvotes: 0

Yunus Kocatas
Yunus Kocatas

Reputation: 316

void main() {
  List a = [2, 3];

  List b = [1, 4];

  List c = [3, 5];

  List d = [];

  for (int i = 0; i < a.length; i++) {
    d.add(a[i] * b[i] * c[i]);
  }
  print(d);
}

Upvotes: 1

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