Less patterns

patterns.less

/* different parameters based on number of elements */
.selector:nth-last-child(2):first-child {
  &, & ~ .selector {
    // setting parameter, i.e.: flex-basis: 50%;
  }
}

.selector:nth-last-child(3):first-child {
  &, & ~ .selector {
    // setting parameter, i.e.: flex-basis: 33.33%;
  }
}

.selector:nth-last-child(4):first-child {
  &, & ~ .selector {
    // setting parameter, i.e.: flex-basis: 25%;
  }
}