Re: Two recursive calls inside of a recursive function

From:
"Jim Langston" <tazmaster@rocketmail.com>
Newsgroups:
comp.lang.c++
Date:
Mon, 10 Mar 2008 14:27:25 -0700
Message-ID:
<cJhBj.523$PO.186@newsfe06.lga>
Jim Langston wrote:

n00m wrote:

This combined with the lack of return-value
makes me wonder what the function is supposed to accomplish.


It's for counting the number of ways to fill a given grid (7x8) with
ciphers 0..6
with all 28 dominos bones. E.g., the answers for these 2 grids:

2
0 3 0 2 2 0 2 3
1 5 6 5 5 1 2 2
3 4 1 4 5 4 4 4
6 6 1 0 5 2 3 0
4 0 3 2 4 1 6 0
1 4 1 5 6 6 3 0
1 2 6 5 5 6 3 3

5 3 1 0 0 1 6 3
0 2 0 4 1 2 5 2
1 5 3 5 6 4 6 4
0 5 0 2 0 4 6 2
4 5 3 6 0 6 1 1
2 3 5 3 4 4 5 3
2 1 1 6 6 2 4 3

are 18 and 1.

Initially I wrote it in Pascal (in that the code works absolutely as
expected, so to speak).


Pascal would pass the entire array to the function, in C and C++
there is no way to pass a native array as a parameter, only some
pointer type ( int[], int*, etc..). If you want to emulate the way
Pascal is doing it, you need to make a copy of the array and pass
that, which is where vector should work for you.

Consider:
#include <vector>
#include <iostream>

typedef std::vector<std::vector<int> > DataType;

void foo(short sch, DataType oc, DataType a, short p, short q, short
fl) {
   // Etc...
}

int main()
{
   DataType a;

   // Size our Data to 10 by 10
   for ( size_t i = 0; i < 10; ++i )
       a.push_back( std::vector<int>(10) );

   for ( size_t i = 0; i < 10; ++i)
       for (size_t j = 0; j < 10; ++j)
           a[i][j] = 7;

   // This makes a copy
   DataType oc = a;

   for ( size_t i = 0; i < 8; ++i) {
       oc[i][7]=1; oc[7][i]=1;
   }

   // Etc...

   // Now, we want to pass a copy to foo, not the original.
   // So make a copy.

   DataType OCCopy = oc;
   DataType ACopy = a;
   foo(1,OCCopy,ACopy,1,1,1);

   // Reset our copies
   OCCopy = oc;
   ACopy = a;
   foo(1,OCCopy,ACopy,1,1,1);

}


Also, it may be better just to make a copy inside of Foo.

void foo(short sch, const DataType oc, const DataType a, short p, short q,
short fl)
{
    DataType OCWorking = oc;
    DataType AWorking = a;
    // Etc...
}

Then change OCWorking and AWorking inside foo to your heart's content, and
the passed in vectors won't be changed, then you don't have to copy them
inside of main. Makes more sense actually.

--
Jim Langston
tazmaster@rocketmail.com

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