二分查找

//二分查找
//要求: 采用左右顺序存储结构,关键字大小有序排列
public int MidSearch(int[] arr,int number int startIndex int endIndex)
{
 if(startIndex>endIndex)
 {
  return -1;
 }
 else
 {
  int mid = (startIndex + endIndex)/2;
  if(arr[mid]>number)
  {
   return MidSearch(arr,number,startIndex,mid -1);
  }
  else if(arr[mid]<number)
  {
   return MidSearch(arr, number,mid+1, endIndex);
  }
  else
  {
   return mid;
  }
 }
}

对于startIndex + endIndex的越界BUG可以利用:

int mid = startIndex+ ((endIndex - startIndex) / 2);

或者:int mid = (startIndex + endIndex) >>> 1;