二分搜索技术

算法描述:

二分搜索算法的基本思想是将n个元素分成个数大致相同的两半,取a[n/2]与x进行比较.如果x=a[x/2],则找到x,算法终止.如果x<a[n/2],则只要在数组a的左半部继续搜索x.如果x>a[n/2],则只要在数组a的右半部继续搜索.

 

实现程序:

/**
 * Copyright (c) 2011 Trusted Software and Mobile Computing(TSMC)
 * All right reserved.
 *
 * Created on 2011
 *
 *		http://jarg.iteye.com/
 *
 */
// Contributors:  Jarg Yee <yeshaoting@gmail.com>
/*
 * TODO 二分搜索
 */
public class BinarySearch
{
	/* 元素序列 */
	private static int[] a = new int[10];
	/* 查找值 */
	private static int x = 3;

	public static void main(String[] args)
	{
		/* 前提条件:数组有序 */
		for(int i=0;i<a.length;i++)
		{
			a[i] = i;
		}
		System.out.println("数组下标:" + binarySearch(0,a.length-1));
		System.out.println("数组下标:" + binarySearch());
	}

	/* 递归求解 */
	private static int binarySearch(int left,int right)
	{
		/* 阈门,无解的情况 */
		if(left>right)
			return -1;
		
		int mid = (left + right)/2;
		if(a[mid]==x)
			return mid;
		else if(a[mid]>x)
			return binarySearch(left,mid-1);
		else if(a[mid]<x)
			return binarySearch(mid+1,right);
		return -1;
	}

	/* 循环求解 */
	private static int binarySearch()
	{
		int left = 0,right = a.length-1;
		while(left<=right)
		{
			int mid = (left+right)/2;
			if(a[mid]==x)
				return mid;
			else if(a[mid]>x)
				right = mid - 1;
			else if(a[mid]<x)
				left = mid + 1;
		}
		return -1;
	}
}