最近用到在list中找出重復(fù)的元素陵且，實(shí)現(xiàn)結(jié)果給大家分享一下，自己也當(dāng)做一個(gè)筆記。
在網(wǎng)上找的布隆過(guò)濾器（BloomFilter）類的實(shí)現(xiàn)：
public class BloomFilter {
private static final int DEFAULT_SIZE = 2 << 24;
private static final int[] seeds = new int[] { 5, 7, 11, 13, 31, 37, 61 };
private BitSet bits = new BitSet(DEFAULT_SIZE);
private SimpleHash[] func = new SimpleHash[seeds.length];
public BloomFilter() {
for (int i = 0; i < seeds.length; i++) {
func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]);
}
}
public void add(String value) {
for (SimpleHash f : func) {
bits.set(f.hash(value), true);
}
}
public boolean contains(String value) {
if (value == null) {
return false;
}
boolean ret = true;
for (SimpleHash f : func) {
ret = ret && bits.get(f.hash(value));
}
return ret;
}
// 內(nèi)部類，simpleHash
public static class SimpleHash {
private int cap;
private int seed;
public SimpleHash(int cap, int seed) {
this.cap = cap;
this.seed = seed;
}
public int hash(String value) {
int result = 0;
int len = value.length();
for (int i = 0; i < len; i++) {
result = seed * result + value.charAt(i);
}
return (cap - 1) & result;
}
}
}
如何使用：
public static void main(String[] args) {
BloomFilter bf = new BloomFilter();
List<String> strs = new ArrayList<String>();
strs.add("123456");
strs.add("hello word");
strs.add("transDocId");
strs.add("123456");
strs.add("transDocId");
strs.add("hello word");
strs.add("test");
for (int i=0;i<strs.size();i++) {
String s = strs.get(i);
boolean bl = bf.contains(s);
if(bl){
System.out.println(i+","+s);
}else{
bf.add(s);
}
}
}
