LeetCode | LRU Cache

来源：互联网发布：集美大学网络编辑：程序博客网时间：2024/04/29 23:19

题目：

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

思路：

问题的关键是实现一个优先队列。由于数组的时间开销太大，我选择了链表以及数列来实现这个优先队列。当然，如果需要更好的性能，可以考虑使用堆栈来实现。

代码：

链表版本

class ListNode1{public:    int key;    int value;    ListNode1* next;    ListNode1(int key, int value)    {        this->key = key;        this->value = value;        next = NULL;    }};class LRUCache{public:    ListNode1 * begin;    int len;    LRUCache(int capacity) {        begin = NULL;        len = capacity;    }        int get(int key) {        if(begin==NULL)            return -1;        if(begin->key == key)        {            return begin->value;        }        else        {            ListNode1* p = begin;            int cur = 1;            while(p->next != NULL&&cur < len)            {                cur++;                if(p->next->key == key)                {                    ListNode1* tmp = p->next;                    p->next = p->next->next;                    tmp->next = begin;                    begin = tmp;                    return begin->value;                }                p=p->next;            };            return -1;        }    }        void set(int key, int value) {        if(begin == NULL)            begin =new ListNode1(key,value);        else        {            ListNode1* p = new ListNode1(key,value);            p->next= begin;            begin=p;            int cur = 1;            while(p->next != NULL&&cur < len)            {                cur++;                if(p->next->key == key)                {                    p->next = p->next->next;                    cur--;                    continue;                }                p=p->next;            };            p->next=NULL;        }    }};

数列版本

class KeyValuePair{public:    int key;    int value;};class LRUCache{public:    KeyValuePair* cache;    int length;    int capacity;    LRUCache(int capacity) {        cache = new KeyValuePair[capacity];        length = 0;        this->capacity = capacity;    }        int get(int key) {        int value = searchAndGetValue(key);                if(value != -1){            insert(key, value);        }                return value;    }        void set(int key, int value) {        searchAndGetValue(key);                if(length == capacity){            remove(0);        }                insert(key, value);    }        int searchAndGetValue(int key){        int result = -1;        for(int i = 0; i < length; i++){            if(cache[i].key == key){                result = cache[i].value;                remove(i);                break;            }        }                return result;    }        void insert(int key, int value){        KeyValuePair tmp;        tmp.key = key;        tmp.value = value;        cache[length++] = tmp;    }        void remove(int index){        for(int i = index; i < length - 1; i++){            cache[i] = cache[i+1];        }        length--;    }};

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