BinarySearch.h

#ifndef CH1_BINARYSEARCH_H
#define CH1_BINARYSEARCH_H

#include <vector>

using std::vector;

/**
 *  The {@code BinarySearch} class provides a static method for binary
 *  searching for an integer in a sorted array of integers.
 *  <p>
 *  The <em>indexOf</em> operations takes logarithmic time in the worst case.
 *  <p>
 *  For additional documentation, see <a href="https://algs4.cs.princeton.edu/11model">Section 1.1</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
class BinarySearch {
public:
    /**
     * This class should not be instantiated.
     */
    BinarySearch() = delete;
    /**
    * Returns the index of the specified key in the specified array.
    *
    * @param  a the array of integers, must be sorted in ascending order
    * @param  key the search key
    * @return index of key in array {@code a} if present; {@code -1} otherwise
    */
    static int indexOf(vector<int> &a, int key) {
        int lo = 0, hi = a.size() - 1;
        while (lo <= hi) {
            // Key is in a[lo..hi] or not present.
            int mid = lo + (hi - lo) / 2;
            if (key < a[mid]) hi = mid - 1;
            else if (key > a[mid]) lo = mid + 1;
            else return mid;
        }
        return -1;
    };
};

#endif //CH1_BINARYSEARCH_H