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MultiMap.java
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144 lines (123 loc) · 4.15 KB
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import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
public class MultiMap<K, V> {
static class Entry<K, V> {
K key;
List<V> values;
public Entry(K key, V value) {
this.key = key;
addValue(value);
}
public Entry(K key, List<V> values) {
this.key = key;
this.values = values;
}
public void addValue(V value) {
if (this.values == null) {
this.values = new ArrayList<>();
}
this.values.add(value);
}
}
private static final float LOAD_FACTOR = 0.75f;
private List<Entry<K, V>>[] buckets;
private int capacity;
private int size;
public MultiMap(int capacity) {
this.capacity = capacity;
this.buckets = new List[this.capacity];
}
public MultiMap() {
this(4);
}
public void put(K key, V value) {
List<Entry<K, V>> bucket = getBucket(key, buckets);
Entry<K, V> entry = getEntry(key, bucket);
if (entry != null) {
entry.addValue(value);
} else {
bucket.add(new Entry<>(key, value));
size++;
if (size >= capacity * LOAD_FACTOR) {
rehash();
}
}
}
public List<V> get(K key) {
List<Entry<K, V>> bucket = getBucket(key, buckets);
Entry<K, V> entry = getEntry(key, bucket);
return entry == null ? null : entry.values;
}
public boolean remove(K key) {
List<Entry<K, V>> bucket = getBucket(key, buckets);
ListIterator<Entry<K, V>> iter = bucket.listIterator();
while (iter.hasNext()) {
Entry<K, V> entry = iter.next();
// Objects.equals(entry.key, key)
if (entry.key == null ? key == null : entry.key.equals(key)) {
iter.remove();
size--;
return true;
}
}
return false;
}
private void rehash() {
this.capacity *= 2;
List<Entry<K, V>>[] newBuckets = new List[this.capacity];
for (List<Entry<K, V>> bucket: buckets) {
if (bucket == null) {
continue;
}
for (Entry<K, V> entry: bucket) {
getBucket(entry.key, newBuckets).add(new Entry<>(entry.key, entry.values));
}
}
this.buckets = newBuckets;
}
private int hash(K key) {
return Math.abs((key == null ? 0 : key.hashCode()) % capacity);
}
private List<Entry<K,V>> getBucket(K key, List<Entry<K,V>>[] buckets) {
int idx = hash(key);
if (buckets[idx] == null) {
buckets[idx] = new LinkedList<>();
}
return buckets[idx];
}
private Entry<K,V> getEntry(K key, List<Entry<K,V>> bucket) {
for (Entry<K, V> entry: bucket) {
if ((entry.key == key) || (entry.key != null && entry.key.equals(key))) {
return entry;
}
}
return null;
}
public static void main(String[] args) {
String[] keys = {"abcdefghijk", "hot", "hot", "dog", "hot", "log", "dog", null, "", null};
Integer[] vals = {1, 23, 4, 5, 6, 7, 8, null, 0, 0};
MultiMap<String, Integer> multiMap = new MultiMap<>();
multiMap.put(null, -1);
System.out.println(multiMap.get(null));
for (int i = 0; i < keys.length; i++) {
multiMap.put(keys[i], vals[i]);
System.out.print(i + ": ");
System.out.println(multiMap.get(keys[i]));
}
String key1 = "hot";
System.out.println(multiMap.remove(key1));
System.out.println(multiMap.get(key1) == null);
System.out.println(!multiMap.remove(key1));
String key2 = null;
System.out.println(multiMap.remove(key2));
System.out.println(multiMap.get(key2) == null);
System.out.println(!multiMap.remove(key2));
for (int i = 0; i < keys.length; i++) {
multiMap.put(keys[i], vals[i]);
System.out.print(i + ": ");
System.out.println(multiMap.get(keys[i]));
}
}
}