二分查找

#include <iostream>
#include <cstdlib>
using namespace std;
/*
 * name : selection sort
 * author : sangoly
 * O(n^2)
 * S(1)
 * date : 2014/4/15
 */
 
 int binary_search(int a[], int v, int low, int high)
 {
      if (low > high)
         return -1;
      int middle = (low+high)/2;
      if (v == a[middle])
         return middle;
      else if (v < a[middle])
         return binary_search(a, v, low, high-1);
      else
         return binary_search(a, v, low+1, high); 
 }
 
 int main(int argc, const char **argv)
 {
     int a[] = {1, 2, 3, 4, 5, 6, 7, 8};
     cout<<binary_search(a, 5, 0, 7)<<endl;
     cout<<binary_search(a, 9, 0, 7)<<endl;
     system("pause");
     return 0;
 }