// binsearch4.cpp
// Glenn G. Chappell
// 22 Feb 2008
//
// For CS 311 Spring 2008
// Binary Search
// Version #4: Iterative (tail recursion eliminated)
// Based on binsearch3.cpp (tail-recursive version)


#include <iostream>
using std::cout;
using std::endl;
#include <cstdlib>    // for std::size_t
#include <algorithm>  // for std::distance, std::advance


// binSearch
// Does Binary Search on a range specified with iterators.
// Requirements on types:
//     FDIter is a forward iterator type.
//     ValueType is the value type of FDIter.
//     operator< is a total order on ValueType.
// Pre:
//     [first, last) is a valid range.
//     Values in the range are sorted by < (ascending).
// Post:
//     Return is true if findMe was found (using equivalence) in range,
//      false otherwise.
// If ValueType operator< throws, then binSearch throws the same exception.
// Otherwise, will not throw.
template <typename FDIter, typename ValueType>
bool binSearch(FDIter first,      // Iterator to first item in range
               FDIter last,       // Iterator to one-past last item in range
               const ValueType & findMe)  // value to find
{
    while (true)  // For tail-recursion elimination
    {
        std::size_t size = std::distance(first, last);

        // BASE CASE (of former recursive function)

        if (size <= 1)
        {
            if (size == 1)
                return !(*first < findMe) && !(findMe < *first);
            else
                return false;
        }

        // RECURSIVE CASE (of former recursive function)

        // Get iterator to middle position of range
        FDIter pivotIter = first;
        std::advance(pivotIter, size/2);

        if (findMe < *pivotIter)
        {   // Recursively search first half of range
            last = pivotIter;
        }
        else
        {   // Recursively search second half of range
            first = pivotIter;
        }

        // Tail-recursive call is gone, replaced by loop
        // return binSearch(first, last, findMe);
    }
}


// Main program
// Demonstrates use of function binSearch
int main()
{
    // Set up array
    const int SIZE = 100000;
    int arr[SIZE];
    for (int i = 0; i < SIZE; ++i)
        arr[i] = 10*i;

    int value = 40;  // Value to search for

    // Do a search
    bool success = binSearch(arr, arr + SIZE, value);

    // Print result
    if (success)
        cout << value << " FOUND" << endl;
    else
        cout << value << " not found" << endl;
}