How to create a function in dart of ArrayCouples

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Have the function ArrayCouples(arr) take the arr parameter being passed which will be an array of an even number of positive integers, and determine if each pair of integers, [k, k+1], [k+2, k+3], etc. in the array has a corresponding reversed pair somewhere else in the array. For example: if arr is [4, 5, 1, 4, 5, 4, 4, 1] then the program should output the string yes because the first pair 4, 5 has the reversed pair 5, 4 in the array, and the next pair, 1, 4 has the reversed pair 4, 1 in the array as well. But if the array doesn't contain all pairs with their reversed pairs, then your program should output a string of the integer pairs that are incorrect, in the order that they appear in the array. For example: if arr is [6, 2, 2, 6, 5, 14, 14, 1] then the program should output the string 5,14,14,1 with only a comma separating the integers.

import 'dart:io';

int ArrayCouples(List arr) {

  
  return arr[0];

}
   
void main() {
  print(ArrayCouples(stdin.readLineSync()));
}

Example:

Input: [2,1,1,2,3,3]
Output: 3,3

So how to create a function like this.

dart
1 Answers

Here's a solution that may work for you, I'll add explanations as comments:

String arrayCouples(List<int> values) {
  // Considers the input having an even number of elements
  assert(values.length % 2 == 0);
  
  // Stores the invalid pairs so we can return them on end
  final List<List<int>> invalidPairs = [];

  // Iterates over even indexes until the last index
  // This will allow us to access a pair using i0 and i0 + 1
  for (int i0 = 0; i0 < values.length; i0 += 2) {
    final int i1 = i0 + 1;

    // Creates the base pair which we'll check on the list
    final List<int> base = [values[i0], values[i1]];
    
    // Stores if the base pair is found in the list
    bool found = false;

    // Set the initial index to iterate backwards
    // If the base pair is the last element on the list,
    // start checking from the last but one pair. If not,
    // start checking from the last pair.
    final int j = (values.length - 1) - ((i0 == values.length - 2) ? 2 : 0);
    
    // Iterates backwards over even indexes until the first index
    // This will allow us to access a pair using j1 and j1 - 1
    for (int j1 = j; j1 - 1 >= 0; j1 -= 2) {
      final int j0 = j1 - 1;

      // Access the current pair
      final List<int> pair = [values[j1], values[j0]];

      // Make the comparison check
      if (base[0] == pair[0] && base[1] == pair[1]) {
        found = true;
        break;
      }
    }

    // If the reversed search doesn't find anything,
    // add the base pair to the invalid pairs
    if (!found) {
      invalidPairs.add(base);
    }
  }

  return invalidPairs.isEmpty 
    // If there are no invalid pairs, return "yes"
    ? "yes"
    // Otherwise, expand all values inside the invalid pairs 
    // to a single list and join them using a comma
    : invalidPairs.expand((pair) => pair).join(",");
}

The output for each one of

print(arrayCouples([4, 5, 1, 4, 5, 4, 4, 1]) == "yes");
print(arrayCouples([6, 2, 2, 6, 5, 14, 14, 1]) == "5,14,14,1");
print(arrayCouples([2, 1, 1, 2, 3, 3]) == "3,3");
print(arrayCouples([2, 1, 1, 2]) == "yes");

is true.

user_99972120
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