第五周作业

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
public class ConsistentHashing {
	/**
	 * 服务器信息集合，key：服务器hash值，value：服务信息（简单用字符串代替）
	 */
	private Map<Integer, String> serverMap = new HashMap<>();
	/**
	 * hash环，存储了环上所有虚拟节点，key：虚拟节点hash值，value：服务器hash值
	 */
	private TreeMap<Integer, Integer> hashRing = new TreeMap<>();
	/**
	 * 每个服务对应虚拟节点数
	 */
	private int                       nodeCount;
	public ConsistentHashing(int nodeCount) {
		if (nodeCount <= 0) {
			//至少有服务本身节点
			this.nodeCount = 1;
			return;
		}
		this.nodeCount = nodeCount;
	}
	/**
	 * 增加服务
	 *
	 * @param serverId 服务标识
	 */
	public void appendServer(String serverId) {
		int serverHash = HashCode.get(serverId);
		if (!serverMap.containsKey(serverHash)) {
			serverMap.put(serverHash, serverId);
			//添加虚拟节点
			for (int i = 0; i < nodeCount; i++) {
				hashRing.put(HashCode.get(serverId + ":VIR" + i), serverHash);
			}
		}
	}
	/**
	 * 移除服务
	 *
	 * @param serverId 服务标识
	 */
	public void removeServer(String serverId) {
		for (int i = 0; i < nodeCount; i++) {
			hashRing.remove(HashCode.get(serverId + ":VIR" + i));
		}
	}
	/**
	 * 获取服务信息
	 *
	 * @param requestKey 请求标识
	 * @return 服务信息
	 */
	public String getServer(String requestKey) {
		if (serverMap.isEmpty()) {
			return null;
		}
		Map.Entry<Integer, Integer> targetNode = hashRing.ceilingEntry(HashCode.get(requestKey));
		if (targetNode == null) {
			targetNode = hashRing.firstEntry();
		}
		return serverMap.get(targetNode.getValue());
	}
}

public class HashCode {
	public static int get(String data){
		return FNVHash1(data);
	}
	private static int FNVHash1(String data)
	{
		final int p = 16777619;
		int hash = (int)2166136261L;
		for(int i=0;i<data.length();i++) {
			hash = (hash ^ data.charAt(i)) * p;
		}
		hash += hash << 13;
		hash ^= hash >> 7;
		hash += hash << 3;
		hash ^= hash >> 17;
		hash += hash << 5;
		return hash;
	}
}

import java.util.Collection;
public class StandardDeviation {
	public static double math(Collection<Integer> datas){
		//求出数组的总和
		double average = datas.stream().mapToInt(Integer::intValue).average().getAsDouble();
		//求出方差
		double var = datas.stream().map(d->(d-average)*(d-average)).mapToDouble(Double::doubleValue).sum();
		//求出标准差
		return Math.sqrt(var/datas.size());
	}
}