二分查找

/*
 * binarySearch.cpp
 * 算法导论 P.23  2.3-5
 *  Created on: 2011-12-27
 *      Author: LiChanghai
 */

#include <iostream>
#include <cstdlib>
 using namespace std;

 template <typename T>
size_t binarySearch(const T array[ ],  size_t pBegin, size_t pEnd, T key)
 {
     //当只有2个元素的时候不再二分，直接比较
     if(pBegin+1 == pEnd)
     {
         if(key == array[pBegin])
             return pBegin;
         else
             if(key == array[pEnd])
                 return pEnd;
             else
             {
                 cerr<<key<<" is not found in this array"<<endl;
                 exit(0);
             }
     }

     //当只有1个元素时，直接比较
     if(pBegin == pEnd)
     {
         if(key == array[pBegin])
             return pBegin;
         else
         {
             cerr<<key<<" is not found in this array"<<endl;
             exit(0);
         }
     }

     size_t pDivide = (pBegin + pEnd)/2; //指向中间位置
     if(key == array[pDivide])
         return pDivide;
     else
         if(key<array[pDivide])
             binarySearch(array, pBegin, pDivide-1, key); //递归调用，在左半部分查找
         else
             binarySearch(array, pDivide+1, pEnd, key); //递归调用，在右半部分查找

 }