算法之二分法查找

二分法检索（binary search）又称折半检索，二分法检索的基本思想是设字典中的元素从小到大有序地存放在数组（array）中，首先将给定值key与字典中间位置上元素的关键码(key)比较，如果相等，则检索成功；否则，若key小，则在字典前半部分中继续进行二分法检索;若key大，则在字典后半部分中继续进行二分法检索。这样，经过一次比较就缩小一半的检索区间，如此进行下去，直到检索成功或检索失败。偶数个取中间2个其中任何一个作为中间元素二分法检索是一种效率较高的检索方法，要求字典在顺序表中按关键码排序。
java 代码 成功返回所在位置，失败返回负数

package ForTest;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Arithmetic{

public static<T extends Comparable<? super T> > int BinarySearch(List<T> array, int start, int end, T key)
{
    int low;
    int high;   
    int guess;

    if(array == null || start>end || start > array.size()-1 || end < 0)
    {
    return -1;
    }  

    start = start < 0 ? 0 : start;
    low  = start-1;

    end = end > array.size()-1 ? array.size()-1 : end; 
    high = end+1; 


        while (high - low > 1) {
            guess = ((high - low)>>1)  + low;

            if (array.get(guess).compareTo(key) < 0)
                low = guess;
            else
                high = guess;
        }

        if (high == end +1 )
        {
         return ~(end +1 );
        }           
        else if (array.get(high).compareTo(key) == 0)
        {
         return high;
        }
        else
        {
        return ~high;
        }      
}
public static<T extends Comparable<? super T> > int BinarySearch(T[] array, int start, int end, T key)
{
List<T> stooges = Arrays.asList(array);
return Arithmetic.BinarySearch(stooges, start, end, key);
}


    public static void main(String[] args) {
// TODO Auto-generated method stub

    ArrayList<Integer> a = new ArrayList<Integer>();

    Float[] b = new Float[100];


    for(int i=0; i<100; i++)
    {
    a.add(i);  
    b[i] = (float) i;

    }    
  System.out.println(""+Arithmetic.BinarySearch(a,0,1000,200));
  System.out.println(""+Arithmetic.BinarySearch(b,0,100,2.f));

}
 }