Train

function train(arr){

  let wagons = arr[0].split(' ').map(Number);
  let maxCapacity = Number(arr[1]);
  let commands = arr.slice(2);

  for(let el of commands){
      let tokens = el.split(' ');

      if(tokens.length === 2){
          wagons.push(+tokens[1]);
      } else{
          let passengersToFit = Number(tokens[0]);

          for(let index in wagons){
              let availableCapacity = maxCapacity - wagons[index];

              if(availableCapacity >= passengersToFit){
                 wagons[index] += passengersToFit;
                 break;
              }
          }
      }
  }
  console.log(wagons.join(' '))
}
train([
   '32 54 21 12 4 0 23',
   '75',
   'Add 10',
   'Add 0',
   '30',
   '10',
   '75'
]);