现在这道题目还只有 9.3%的AC率，难度为Hard
Total Accepted: 9
Total Submissions: 97
Difficulty: Hard

https://leetcode.com/problems/all-oone-data-structure/

class AllOne {

    // Hashmap for get Node to operate inc and dec
    // LinkNode to maintain order
    // HashSet to maintain key with certain value

    private class LinkNode {
        public int val; // maintain current value
        LinkNode small; // maintain link to smaller node
        LinkNode big; // maintain link to bigger node
        Set<String> keySet; // maintain keys with current value

        LinkNode(String key, int v) {
            keySet = new HashSet<>();
            keySet.add(key);
            val = v;
        }
    }

    private LinkNode maxNode;
    private LinkNode minNode;
    Map<String, LinkNode> hmap;

    /** Initialize your data structure here. */
    public AllOne() {
        hmap = new HashMap<>();
        maxNode = null;
        minNode = null;
    }

    /** Inserts a new key <Key> with value 1. Or increments an existing key by 1. */
    public void inc(String key) {
        LinkNode lknd;

        if (hmap.containsKey(key)) {
            lknd = hmap.get(key);
            lknd.keySet.remove(key);

            if (lknd.big != null) {
                if (lknd.big.val == lknd.val+1) {
                    lknd.big.keySet.add(key);
                    hmap.put(key, lknd.big);
                }
                else {
                    LinkNode lbig = new LinkNode(key, lknd.val+1);
                    lbig.small = lknd;
                    lbig.big = lknd.big;
                    lknd.big = lbig;
                    lbig.big.small = lbig;
                    hmap.put(key, lbig);
                }
            }
            else {
                LinkNode lbig = new LinkNode(key, lknd.val+1);
                lbig.small = lknd;
                lknd.big = lbig;
                maxNode = lbig;
                hmap.put(key, lbig);
            }

            // remove original node if necessary
            if (lknd.keySet.isEmpty()) {
                // for minNode
                if (minNode == lknd) {
                    minNode = lknd.big;
                }
                else {
                    lknd.small.big = lknd.big;
                }
                // for maxNode
                if (maxNode == lknd) {
                    maxNode = lknd.small;
                }
                else {
                    lknd.big.small =lknd.small;
                }
            }
        }
        else {
            if (minNode == null) {
                // all list is null
                lknd = new LinkNode(key, 1);
                minNode = lknd;
                maxNode = lknd;
            }
            else {
                if (minNode.val != 1) {
                    lknd = new LinkNode(key, 1);
                    lknd.big = minNode;
                    minNode.small = lknd;
                    minNode = lknd;
                }
                else {
                    minNode.keySet.add(key);
                    lknd = minNode;
                }
            }
            hmap.put(key, lknd);
        }
    }

    /** Decrements an existing key by 1. If Key‘s value is 1, remove it from the data structure. */
    public void dec(String key) {
        LinkNode lknd;

        if (hmap.containsKey(key)) {
            lknd = hmap.get(key);
            lknd.keySet.remove(key);

            if (lknd.val == 1) {
                hmap.remove(key);
            }
            else {
                if (lknd.small != null) {
                    if (lknd.small.val == lknd.val - 1) {
                        lknd.small.keySet.add(key);
                        hmap.put(key, lknd.small);
                    }
                    else {
                        LinkNode lsmall = new LinkNode(key, lknd.val - 1);
                        lsmall.big = lknd;
                        lsmall.small = lknd.small;
                        lknd.small = lsmall;
                        lsmall.small.big = lsmall;
                        hmap.put(key, lsmall);
                    }
                }
                else {
                    LinkNode lsmall = new LinkNode(key, lknd.val - 1);
                    lknd.small = lsmall;
                    lsmall.big = lknd;
                    minNode = lsmall;
                    hmap.put(key, lsmall);
                }
            }

            // remove original node if necessary
            if (lknd.keySet.isEmpty()) {
                // for minNode
                if (minNode == lknd) {
                    minNode = lknd.big;
                }
                else {
                    lknd.small.big = lknd.big;
                }
                // for maxNode
                if (maxNode == lknd) {
                    maxNode = lknd.small;
                }
                else {
                    lknd.big.small =lknd.small;
                }
            }

        }
    }

    /** Returns one of the keys with maximal value. */
    public String getMaxKey() {
        if (maxNode == null) {
            return "";
        }
        Iterator<String> iter = maxNode.keySet.iterator();
        return iter.next();
    }

    /** Returns one of the keys with Minimal value. */
    public String getMinKey() {
        if (minNode == null) {
            return "";
        }
        Iterator<String> iter = minNode.keySet.iterator();
        return iter.next();
    }

    public void printAll() {
        LinkNode tmp = maxNode;
        System.out.println("Start print");
        if (tmp != null) {
            System.out.printf("Node val: %d\n", tmp.val);
            Iterator<String> iter = tmp.keySet.iterator();
            while (iter.hasNext()) {
                System.out.printf("key: %s,", iter.next());
            }
            System.out.println();
            tmp = tmp.small;
        }
        if (minNode != null) {
            System.out.printf("Min Node val: %d\n", minNode.val);
            Iterator<String> iter = minNode.keySet.iterator();
            while (iter.hasNext()) {
                System.out.printf("key: %s,", iter.next());
            }
            System.out.println();
        }
        System.out.println("End print");
    }
}

    /**
     * Your AllOne object will be instantiated and called as such:
     * AllOne obj = new AllOne();
     * obj.inc(key);
     * obj.dec(key);
     * String param_3 = obj.getMaxKey();
     * String param_4 = obj.getMinKey();
     */