你的问题还需要进一步澄清：

• subtraction = 700的输出应该是什么？
• subtraction = 600的输出应该是什么？
• subtraction = 100的输出应该是什么？

以下内容可以作为解决您问题的起点：

fun subtraction() {
  var subtraction = 250
  var list = mutableListOf(300, 200, 100)
  // Loop the list in Reverse order
  for (number in list.indices.reversed()) {
    subtraction -= list[number] // Subtract the last number
    // If subtraction is greater than zero, continue and remove the last element
    if (subtraction > 0)
      list.removeAt(number)
    else {
      // It subtraction is less than or equal to zero, 
      // remove the last element, append the final subtraction result, 
      // and stop the loop
      list.removeAt(number)
      list.add(abs(subtraction))
      break
    }
  }
  // If the subtraction result is still positive after whole list has been processed, 
  // append it back to the list
  // if (subtraction > 0)
  //   list.add(subtraction)
  println(list)
}

产出

[300, 50]