Reduction in Java

Similarly,two ways are available if we wanted to reduce a list.

Wired-in versions of reduce, based on a binary function B and a unit U:

Recursive version of reduce:

static int reduce(intList L)

{

if( isEmpty(L) )

  return U;

return B(first(L), reduce(rest(L)));

}

 

Recursive version of reduce using accumulator:

This function would be called at the outset as

reduce(L, U)

i.e. U is the value of the accumulator in the outermost call

static int reduce(intList L, int Acc)

{

if( isEmpty(L) )

  return Acc;

return reduce(rest(L), B(Acc, first(L)));

}

 

Iterative version of reduce:

static int reduce(intList L)

{

int Acc = U;		// Unit

while( !isEmpty(L) )

  {

  Acc = B(Acc, first(L));

  L = rest(L);

  }

return Acc;

}