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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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

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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

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