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Copy pathAllOoneDataStructure.java
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116 lines (104 loc) · 3.74 KB
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import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
// hashmap + double linked list
class AllOne {
// maintain a doubly linked list of Buckets
private Bucket head;
private Bucket tail;
// for accessing a specific Bucket among the Bucket list in O(1) time
private Map<Integer, Bucket> countBucketMap;
// keep track of count of keys
private Map<String, Integer> keyCountMap;
// each Bucket contains all the keys with the same count
private class Bucket {
int count;
Set<String> keySet;
Bucket next;
Bucket pre;
public Bucket(int cnt) {
count = cnt;
keySet = new HashSet<>();
}
}
/** Initialize your data structure here. */
public AllOne() {
head = new Bucket(Integer.MIN_VALUE);
tail = new Bucket(Integer.MAX_VALUE);
head.next = tail;
tail.pre = head;
countBucketMap = new HashMap<>();
keyCountMap = new HashMap<>();
}
/** Inserts a new key <Key> with value 1. Or increments an existing key by 1. */
public void inc(String key) {
if (keyCountMap.containsKey(key)) {
changeKey(key, 1);
} else {
keyCountMap.put(key, 1);
if (head.next.count != 1)
addBucketAfter(new Bucket(1), head);
head.next.keySet.add(key);
countBucketMap.put(1, head.next);
}
}
/** Decrements an existing key by 1. If Key's value is 1, remove it from the data structure. */
public void dec(String key) {
if (keyCountMap.containsKey(key)) {
int count = keyCountMap.get(key);
if (count == 1) {
keyCountMap.remove(key);
removeKeyFromBucket(countBucketMap.get(count), key);
} else {
changeKey(key, -1);
}
}
}
/** Returns one of the keys with maximal value. */
public String getMaxKey() {
return tail.pre == head ? "" : (String) tail.pre.keySet.iterator().next();
}
/** Returns one of the keys with Minimal value. */
public String getMinKey() {
return head.next == tail ? "" : (String) head.next.keySet.iterator().next();
}
// helper function to make change on given key according to offset
private void changeKey(String key, int offset) {
int count = keyCountMap.get(key);
keyCountMap.put(key, count + offset);
Bucket curBucket = countBucketMap.get(count);
Bucket newBucket;
if (countBucketMap.containsKey(count + offset)) {
// target Bucket already exists
newBucket = countBucketMap.get(count + offset);
} else {
// add new Bucket
newBucket = new Bucket(count + offset);
countBucketMap.put(count + offset, newBucket);
addBucketAfter(newBucket, offset == 1 ? curBucket : curBucket.pre);
}
newBucket.keySet.add(key);
removeKeyFromBucket(curBucket, key);
}
private void removeKeyFromBucket(Bucket bucket, String key) {
bucket.keySet.remove(key);
if (bucket.keySet.size() == 0) {
removeBucketFromList(bucket);
countBucketMap.remove(bucket.count);
}
}
private void removeBucketFromList(Bucket bucket) {
bucket.pre.next = bucket.next;
bucket.next.pre = bucket.pre;
bucket.next = null;
bucket.pre = null;
}
// add newBucket after preBucket
private void addBucketAfter(Bucket newBucket, Bucket preBucket) {
newBucket.pre = preBucket;
newBucket.next = preBucket.next;
preBucket.next.pre = newBucket;
preBucket.next = newBucket;
}
}