随机数生成

/**
 * GetRandomNum.java
 */
package Algorithm;

import java.util.Arrays;
import java.util.Random;

import org.junit.Test;

/**
 * @Author: chenxiaoyu
 * @Date:   2013-8-4下午4:19:04
 * @Description:
 */
public class RandomNum {

	@Test
	public void randomTest(){
		int[] array = getRandom(10,30,20);
		Arrays.sort(array);
		print(array);
	}
	
	//生成大于等于begin小于end且没有重复的count个整数的问题
	public static int[] getRandom(int begin, int end, int count){
		if(count > end - begin){
			System.out.println("error! Can't generate enough not repeated " + count +" nums between " + begin + " and " + end);
		}
		int[] array = new int[count];
		int total = 0;
		while(total < count){
			Random random = new Random();
			int num = random.nextInt(end-begin) + begin;
			for(int i=0; i<count; i++){
				if(array[i] == num)
					break;
				if(i == count-1){
					array[total] = num;
					total ++;
				}
			}
		}
		print(array);
		return array;
	}
	
	private static void print(int[] array){
		System.out.println("\n" + "length :" + array.length);
		for(int i=0;i<array.length;i++){
			System.out.print(array[i] + " ");
		}
	}
	
	/*---------------------------------------------------------------------------------------------------------------------
	*/
	
	
	//编程珠玑12章 输入两个整数m和n,m<n，输出是0~n-1范围内的m个随机整数的有序列表，不允许重复。从概率角度说，我们希望得到没有重复的有序选择，其中每个出现的选择概率相等。
	public void getknuth(int m,int n){
		for(int i=0; i<n; i++){
			//在剩余的n-i中选择m
			Random random = new Random();
			if(random.nextInt(n*10) % (n-i) < m){
				System.out.println(i);
				m--;
			}
		}
	}
	
	@Test
	public void test(){
		getknuth(100,100000);
	}
}