微信红包算法遐想

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 private final AtomicLong seed;    private static final long multiplier = 0x5DEECE66DL;    private static final long addend = 0xBL;    private static final long mask = (1L << 48) - 1;    /**     * Creates a new random number generator. This constructor sets     * the seed of the random number generator to a value very likely     * to be distinct from any other invocation of this constructor.     */    public Random() {        this(seedUniquifier() ^ System.nanoTime());    }

闲来无事，想如果自己设计微信红包，怎么设计呢？

因为我不是微信红包的开发人员，所以以下内容纯属虚构

先说下我的算法，每人随机一个数，然后把所有人的加起来成为分母，每个人的数是分子，分子除以分母，就是这个人占用红包的额度。

直接看代码

public class Haobao {public static List<Integer> buildFen(int fen,int i){if(fen<=i){return null;}List<Integer> ins=new ArrayList<Integer>(i);List<Integer> cns=new ArrayList<Integer>(i);//Random r=ThreadLocalRandom.current();Random r=new Random();int total=0;for(int j=0;j<i;j++){int c=r.nextInt(i*10)+1;total=total+c;ins.add(c);}BigDecimal t=new BigDecimal(total);BigDecimal f=new BigDecimal(fen);BigDecimal s=f.divide(t,4,BigDecimal.ROUND_DOWN);for(int j=0;j<i-1;j++){int c=s.multiply(new BigDecimal(ins.get(j))).intValue();if(c==0||(fen-c)<(i-j)){c=1;}fen=fen-c;cns.add(c);}cns.add(fen);return cns; } public static void main(String[] args){for(int k=0;k<10;k++){long begin=System.currentTimeMillis();for(int i=0;i<10*10000;i++){List<Integer> s=buildFen(2245, 100);//System.out.println(s.toString());}System.out.println("time:"+(System.currentTimeMillis()-begin));}}}

Random VS ThreadLocalRandom

有人说ThreadLocalRandom 性能比Random高，有人说Random线程不安全。

今天就看下源码，本人看的是JDK 1.7的

先看Random的，关键是seed因子

 private final AtomicLong seed;    private static final long multiplier = 0x5DEECE66DL;    private static final long addend = 0xBL;    private static final long mask = (1L << 48) - 1;    /**     * Creates a new random number generator. This constructor sets     * the seed of the random number generator to a value very likely     * to be distinct from any other invocation of this constructor.     */    public Random() {        this(seedUniquifier() ^ System.nanoTime());    }

再看下ThreadLocalRandom ,首先ThreadLocalRandom 继承了Random，仔细看接口，一些方法都是重用父类的。

用TheadLocal 实现的线程安全。

    private static final ThreadLocal<ThreadLocalRandom> localRandom =        new ThreadLocal<ThreadLocalRandom>() {            protected ThreadLocalRandom initialValue() {                return new ThreadLocalRandom();            }    };

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