implement the next function of interable to iterate over a 2D array in kotlin-CodePudding

I have a custom class that is array<array<K>>. I want to iterate over it with forEach, you know, the way we do with arrays in kotlin. I implement the iterable<k> and the hasNext function is easy. Problem is, the next function is hard because now I have columns and the columns are of different sizes. I would appreciate it if you could tell me how to write next(). Some hints in the right direction is fine.

CodePudding user response：

here is an example of the next() function of an Iterable class that iterates over a 2D array in Kotlin:

class Array2DIterable<T>(val array: Array<Array<T>>) : Iterable<T> {
override fun iterator(): Iterator<T> {
    return object : Iterator<T> {
        var x = 0
        var y = 0

        override fun hasNext(): Boolean {
            return x < array.size && y < array[x].size
        }

        override fun next(): T {
            val next = array[x][y]
            y  
            if (y >= array[x].size) {
                y = 0
                x  
            }
            return next
        }
    }
}}

You can test it like this :

val array = arrayOf(
    arrayOf(1, 2, 3),
    arrayOf(4, 5, 6),
    arrayOf(7, 8, 9)
)
val iterable = Array2DIterable(array)
for (element in iterable) {
    println(element)
}

This is the output for this sample test case

Hope it'll help sort it out.

CodePudding user response：

Here is the answer to my own question. In fact, I am doing this as a self-set exercise to a tutorial about coding a hashmap.

  override fun iterator(): Iterator<K> {
  return object : Iterator<K> {
   var stopLoopNumber = 0
   var rowEntry = 0
   var columnEntry = 0

   override fun hasNext(): Boolean {
    return stopLoopNumber < getAllEntries()
   }

   override fun next(): K {
    //check if a row has more than one entry. if so, increment the column to output all entries in the column.
    //at the same time increment the stopLoopNumber each time an entry is output.
    return if (columnEntry < entries[rowEntry].size) {
     stopLoopNumber  
     entries[rowEntry][columnEntry  ].key
    } else {
     // the column is exhausted, so reset it to 0, ready for the next row.
     columnEntry = 0
     stopLoopNumber  
     //move to the next row and after outputting the entry, increment the column. This is vital because we must
     //increment the column after an entry is output.
     entries[  rowEntry][columnEntry  ].key
    }
   }
  }
 }