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Searching an element in a sorted array

Solutons:


I would have a few concerns about hiring someone who submitted this for a code sample. Here is what I see.

First, addressing overall design, the algorithm is suboptimal, and is worst case linear instead of worst case logarithmic, because it doesn’t use a binary search to find the amount of elements, but a linear one.

Second, (and this is what would have really killed it for me) the variable names. Most of these are either one or two letters, and the code is very unreadable because of it. Giving your variables descriptive names is important for maintainability.

Third, ignoring standard libraries. Unless instructed not to use them, you should prefer standard libraries which have implementations of binary search (e.g. the stl or bsearch)

Fourth, why have get_num_of_ints return -1 has a magic value feeling to me; better to just set count = 0 and check that.

Fifth, get_num_of_ints is just far too long, and tries to do way too much. It badly needs to be broken up.

Sixth (and this is a personal choice), I think C++, with the STL, is a far better choice in this instance.

In the spirit of “show, don’t tell”, here is how I would have written the assignment (untested, uncompiled) (edited to match the required function signature):

#include <iostream>
#include <algorithm>

using namespace std;

// This function signature is required:
int get_num_of_ints(const int* searchBegin, size_t searchSize, int input,
    size_t* first, size_t* count) {
  const int* searchEnd = searchBegin + searchSize;
  const int* result = lower_bound(searchBegin, searchEnd, input);

  if (searchEnd == result || *result != input)
    return -1;

  *first = result - searchBegin;
  *count = upper_bound(result, searchEnd, input) - result;
  return 0;
}

void print_search_results(const int* searchBegin, size_t searchSize, int input) {
  size_t first;
  size_t count; 

  if (get_num_of_ints(searchBegin, searchSize, input, &first, &count) < 0) {
    cout << input << " is not in the array." << endl;
    return;
  }

  cout << input << " was found at index " << first << ". "
       << "There are " << count << " instances for " << input << " in the array."
       << endl;
}

bool read_input(int* input) {
  cout << "Enter a number to search for: ";
  bool succeeded = cin >> *input;
  cout << endl;    
  return succeeded;
}

int main (int argc, char** argv) {
  const int searchNumbers[] = {1, 2, 4, 4, 5, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 11, 13};
  const int searchNumbersSize = sizeof(searchNumbers)/sizeof(searchNumbers[0]);

  while(1) {
     int input;
     if(!read_input(&input)) {
       count << "Bad input, exiting" << endl;
       return 1;
     }

     print_search_results(searchNumbers, searchNumbersSize, input);
  }
}

In my experience, the

if (condition)
    consequence;
statementx;
...

style is a land mine just waiting for another (or even the same) developer to extend it to:

if (condition)
    consequence1;
    consequence2;
statementx;
...

Some of you might see what the problem is, but for most programmers, it is a virtually invisible bug because developers tend to interpret code by indentation even though the curly braces are missing, making consequence2 unconditional.

In addition to many of the other comments, the following:

m = (hi + lo)/2;

is the wrong way to find the middle index. This can overflow. You should do:

m = lo + (hi - lo) / 2;

Second, the line:

m=m;

has no effect, and can be eliminated.

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