实现一个数据结构支持以下操作:
1. Inc(key) - 插入一个新的值为 1 的 key。或者使一个存在的 key 增加一,保证 key 不为空字符串。
2.Dec(key) - 如果这个 key 的值是 1,那么把他从数据结构中移除掉。否者使一个存在的 key 值减一。如果这个 key 不存在,这个函数不做任何事情。key 保证不为空字符串。
3.GetMaxKey() - 返回 key 中值最大的任意一个。如果没有元素存在,返回一个空字符串""。
4.GetMinKey() - 返回 key 中值最小的任意一个。如果没有元素存在,返回一个空字符串""。
挑战:以 O(1) 的时间复杂度实现所有操作。
详见:https://leetcode.com/problems/all-oone-data-structure/description/
C++:
class AllOne { public: /** Initialize your data structure here. */ AllOne() {} /** Inserts a new key <Key> with value 1. Or increments an existing key by 1. */ void inc(string key) { if (!m.count(key)) { if (buckets.empty() || buckets.back().val != 1) { auto newBucket = buckets.insert(buckets.end(), {1, {key}}); m[key] = newBucket; } else { auto newBucket = --buckets.end(); newBucket->keys.insert(key); m[key] = newBucket; } } else { auto curBucket = m[key], lastBucket = (--m[key]); if (lastBucket == buckets.end() || lastBucket->val != curBucket->val + 1) { auto newBucket = buckets.insert(curBucket, {curBucket->val + 1, {key}}); m[key] = newBucket; } else { lastBucket->keys.insert(key); m[key] = lastBucket; } curBucket->keys.erase(key); if (curBucket->keys.empty()) buckets.erase(curBucket); } } /** Decrements an existing key by 1. If Key's value is 1, remove it from the data structure. */ void dec(string key) { if (!m.count(key)) return; auto curBucket = m[key]; if (curBucket->val == 1) { curBucket->keys.erase(key); if (curBucket->keys.empty()) buckets.erase(curBucket); m.erase(key); return; } auto nextBucket = ++m[key]; if (nextBucket == buckets.end() || nextBucket->val != curBucket->val - 1) { auto newBucket = buckets.insert(nextBucket, {curBucket->val - 1, {key}}); m[key] = newBucket; } else { nextBucket->keys.insert(key); m[key] = nextBucket; } curBucket->keys.erase(key); if (curBucket->keys.empty()) buckets.erase(curBucket); } /** Returns one of the keys with maximal value. */ string getMaxKey() { return buckets.empty() ? "" : *(buckets.begin()->keys.begin()); } /** Returns one of the keys with Minimal value. */ string getMinKey() { return buckets.empty() ? "" : *(buckets.rbegin()->keys.begin()); } private: struct Bucket { int val; unordered_set<string> keys; }; list<Bucket> buckets; unordered_map<string, list<Bucket>::iterator> m; }; /** * 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(); */
参考:https://www.cnblogs.com/grandyang/p/6012229.html