折半查找

import java.util.Arrays;


public class ArratTest5 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] arr=new int[]{1,2,4,2,6,3,5,7,3,9};
		//int index=getIndex(arr,11);
		Arrays.sort(arr);
		printArray(arr);
		int index=halfSearch_2(arr,2);
		System.out.println("index="+index);
	}
	//第二种半分算法
	public static int halfSearch_2(int[] arr,int key)
	{
		int min=0,max=arr.length-1,mid;
		while(min<=max)
		{
			mid=(max+min)/2;
			if(key>arr[mid])
				min=mid+1;
			else if(key<arr[mid])
				max=mid-1;
			else return mid;
		}
		return -1;
	}
	//第一种半分算法
	public static int halfSearch(int[] arr,int key)
	{
		int min,max,mid;
		min=0;
		max=arr.length-1;
		mid=(min+max)/2;
		while(arr[mid]!=key)
		{
			if(arr[mid]<key)
				min=mid+1;
			else if(key<arr[mid])
				max=mid-1;
			if(min>max)
					return -1;
			mid=(min+max)/2;
		}
		return mid;
	}
	public static int getIndex(int[] arr,int key)
	{
		for(int x=0;x<arr.length;x++)
		{
			if(arr[x]==key)
				return x;
		}
		return -1;
	}
	public static void printArray(int[] arr)
	{
		System.out.print("[");
		for(int x=0;x<arr.length;x++)
		{
			if(x!=arr.length-1)
				System.out.print(arr[x]+", ");
			else
				System.out.println(arr[x]+"]");
		}
	}
}