二分法查找

判断x是否在该数组中。

int binSearch(int a[ ], int low, int high, int x)
{ while(low<=high)
 { mid=(low+high)/2;
  if(x==a[mid]) return mid;
  if(x>a[mid]) low = mid+1;
   else    high=mid - 1;
 }
 return -1;
}