Two Recursively Searching Algorithms - and one really annoying bug!

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October 10th, 2002, 05:20 PM

supaben34

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Two Recursively Searching Algorithms - and one really annoying bug!

Hey all,
I have a problem with a recursive algorithm. I actually need help with two of them:
One is the recursive sequential search and the other is the recursive binary search. I am about to place a lot of code on the screen so watch out now.

Code:

#include "hw4Lib.h"
#include <string>

void printArray(int* array, int arraySize)
{
  cout << "[";
  for (int i = 0; i < arraySize - 1; i++)
  {
    cout << array[i] << ", ";
  }
  cout << array[arraySize - 1] << "]";
}

int main()
{
  int unsortedList[8] = {3, 8, 5, 7, 2, 1, 4, 6};
  int unsortedList2[7] = {3, 8, 5, 7, 2, 1, 4};
  //int sortedList[8] = {1, 2, 3, 4, 5, 6, 7, 8};
  //int sortedList2[7] = {1, 2, 3, 4, 5, 6, 7};
  int item1 = 7;
  int item2 = 4;
  int item3 = 9;
  int arraySize = 8;
  int arraySize2 = 7;

  cout << "sequentialSearch(" << item2 << ", ";
  printArray(unsortedList2, arraySize2); 
  cout << ", " << arraySize2 << ") = ";
  cout << sequentialSearch(item2, unsortedList2, arraySize2) << "\n";

  cout << "sequentialSearch(" << item1 << ", ";
  printArray(unsortedList, arraySize); 
  cout << ", " << arraySize << ") = ";
  cout << sequentialSearch(item1, unsortedList, arraySize) << "\n";

  cout << "sequentialSearch(" << item3 << ", ";
  printArray(unsortedList, arraySize); 
  cout << ", " << arraySize << ") = ";
  cout << sequentialSearch(item3, unsortedList, arraySize) << "\n\n";

  //cout << "binarySearch(" << item2 << ", ";
  //printArray(sortedList2, arraySize2); 
  //cout << ", " << arraySize2 << ") = ";
  //cout << binarySearch(item2, sortedList2, arraySize2) << "\n";

  //cout << "binarySearch(" << item1 << ", ";
  //printArray(sortedList, arraySize); 
  //cout << ", " << arraySize << ") = ";
  //cout << binarySearch(item1, sortedList, arraySize) << "\n";

  //cout << "binarySearch(" << item3 << ", ";
  //printArray(sortedList, arraySize); 
  //cout << ", " << arraySize << ") = ";
  //cout << binarySearch(item3, sortedList, arraySize) << "\n";
}

The above is the driver. Below is the recursive sequential search that I got so far.

Code:

#include "hw4Lib.h"

//'listSize' is a parameter that inputs size of the array into function 
//'item' is a parameter that inputs the current value of the function
//list is a pointer to the array

int sequentialSearch(int item, int *list, int listSize)
{
  if (listSize == 0)
    return -1;
  if (*list == item)
    return listSize - 2;
  else
    list++;
  return sequentialSearch(item, list, listSize - 1);
}

And below is my hw4Lib.h. Yes, this is for one of my courses but hey you gotta gimme an A for trying and I am so close too.

Code:

#include <iostream.h> 

  int sequentialSearch(int item, int* list, int listSize);
  int binarySearch(int item, int* list, int listSize);

It almost works guys... I just can't get it to read the right answers for the first sequential_search. OOps almost forgot what the answer should be This program basically searches for a specific integer and the answer would be whatever position the integer is in (starting from 0 of course..) If the integer is not in the array then it should print out a -1.

I got the last two tests correct, just not the first one. Please help.

And just to make things a little bit more challenging I need to do the binary search also. Any help at all would be appreciated. I thank you all in advance.

October 10th, 2002, 06:36 PM

Scorpions4ever

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Here's one way for the sequential search:
Change sequentialSearch to accept a fourth param, the full size of the array.

Code:

int int sequentialSearch(int item, int *list, int listSize, int fullSize)
{

  if (listSize == 0)
    return -1;
  if (*list == item)
    return fullSize - listSize;
  else
    list++;
  return sequentialSearch(item, list, listSize - 1, fullSize);
}

and in function main(), change the calls to

Code:

  cout << "sequentialSearch(" << item2 << ", ";
  printArray(unsortedList2, arraySize2);
  cout << ", " << arraySize2 << ") = ";
  cout << sequentialSearch(item2, unsortedList2, arraySize2, arraySize2) << "\n";

  cout << "sequentialSearch(" << item1 << ", ";
  printArray(unsortedList, arraySize);
  cout << ", " << arraySize << ") = ";
  cout << sequentialSearch(item1, unsortedList, arraySize, arraySize) << "\n";

  cout << "sequentialSearch(" << item3 << ", ";
  printArray(unsortedList, arraySize);
  cout << ", " << arraySize << ") = ";
  cout << sequentialSearch(item3, unsortedList, arraySize, arraySize) << "\n\n";

Note that I made sequentialSearch return the index of a 0 based array (since you're returning -1 on failure). Hope this helps!

October 10th, 2002, 06:55 PM

supaben34

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Location: Tallahassee

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THANK YOU SO MUCH FOR ALL THOSE WHO HELPED! I GOT IT DONE!(Sorry about the caps) but I am just so blasted excited! There's nothing like the feeling that comes over you when you program compiles from scratch...nothing can beat it. Thank again.

October 10th, 2002, 06:59 PM

Scorpions4ever

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Location: Woodland Hills, Los Angeles County, California, USA

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Here's my implementation of binarySearch:

Code:

int binarySearch(int item, int *list, int listStart, int listEnd)
{
  int midPoint = (listStart + listEnd) / 2;
  if (*(list + midPoint) == item)
    return midPoint;
  else if (midPoint == listStart)
    return -1;
  else if (*(list + midPoint) < item)
    return binarySearch(item, list, midPoint, listEnd);
  else if (*(list + midPoint) > item)
    return binarySearch(item, list, listStart, midPoint);
}

Change the calls in main() to:

Code:

  cout << "binarySearch(" << item2 << ", ";
  printArray(sortedList2, arraySize2);
  cout << ", " << arraySize2 << ") = ";
  cout << binarySearch(item2, sortedList2, 0, arraySize2) << "\n";

  cout << "binarySearch(" << item1 << ", ";
  printArray(sortedList, arraySize);
  cout << ", " << arraySize << ") = ";
  cout << binarySearch(item1, sortedList, 0, arraySize) << "\n";

  cout << "binarySearch(" << item3 << ", ";
  printArray(sortedList, arraySize);
  cout << ", " << arraySize << ") = ";
  cout << binarySearch(item3, sortedList, 0, arraySize) << "\n";

and change the prototypes in hw4Lib.h to

Code:

int sequentialSearch(int item, int* list, int listSize, int fullSize);
int binarySearch(int item, int* list, int listStart, int listEnd);

Hope this helps!

October 10th, 2002, 07:18 PM

supaben34

Contributing User

Join Date: Jul 2002

Location: Tallahassee

Posts: 55

Time spent in forums: 2 h 57 m 51 sec
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A little problem...

There seems to be a problem. I read back on the program requirements and it seems like the only files that can be edited is the hw4Lib.cpp and hw4Lib.h which means that I cannot change the other files. Is there any way to get around this and retain the same functionality?

October 11th, 2002, 01:38 AM

Scorpions4ever

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I can think of a couple of ways at least. Before I come up with solutions though, can you please verify a few things for me:
1. Do these functions have to be recursive.
2. Can these functions call other functions (i.e.) can I write:
int sequentialSearch2(int item, int *list, int listSize, int fullSize)
and then make sequentialSearch call sequentialSearch2 like this:
int sequentialSearch(int item, int *list, int listSize) {
return sequentialSearch2(item, list, listSize, listSize);
}
This way, main() does not need to be modified at all

3. Are you allowed use other C++ features such as default parameter values for functions?
4. Can you do creative things with #define. Specifically, what if you do something like this in hw4Lib.h
#define sequentialSearch(a, b, c) sequentialSearch2(a, b, c, c)
This way, you're not altering the file containing main() directly, but since hw4Lib.h is #included in the file containing main(), you are using the C pre-processor to alter the code for you.

There's more than one way to get around not modifying the file containing main(), depending on how you want to bend the rules

Two Recursively Searching Algorithms - and one really annoying bug!

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