java 二分查找算法

编程之美在于算法之美，先来看看二分查找的算法：

隐藏条件：二分查找必须是有序的，从小到大，或从大到小的排序才能进行二分查找，下面来看看代码：

package com.cn.daming;

public class MainActivity {
	

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		int[] aInts = new int[]{1,3,5,8,11,14,16,24,37,47,49,56,63,83,223}; //排序是从小到大
		int[] aInts2 = new int[]{322,243,211,156,98,85,79,68,53,47,38,24,13,6,2}; //排序是从大到小
		// TODO Auto-generated method stub
		MainActivity main = new MainActivity();
		System.out.println("aInts  the reault is : " + main.binarySearch(aInts, 0, aInts.length, 24));
		System.out.println("aInts2 the reault is : " + main.binarySearch2(aInts2, 0, aInts2.length, 243));
	}

	//从小到大的二分查找
	private int binarySearch(int[] a, int start, int len, int key) {
        int high = start + len, low = start - 1, guess;

        while (high - low > 1) {
            guess = (high + low) / 2;

            if (a[guess] < key)
                low = guess;
            else
                high = guess;
        }

        if (high == start + len)
            return ~(start + len);
        else if (a[high] == key)
            return high;
        else
            return ~high;
    }
	
	//从大到小的二分查找
	private int binarySearch2(int[] a, int start, int len, int key) {
        int high = start + len, low = start - 1, guess;

        while (high - low > 1) {
            guess = (high + low) / 2;

            if (a[guess] > key)
                low = guess;
            else
                high = guess;
        }

        if (high == start + len)
            return ~(start + len);
        else if (a[high] == key)
            return high;
        else
            return ~high;
    }
}

返回值就是返回要查的key的下标；

看结果如图：