链表&LRU

简介

链表就是链式存储数据的一种数据结构。双向链表每个数据存储都包含他的前后数据节点的位置信息（索引/指针）。

   class DSChain<T>
    {
        //使用栈来进行废弃空间回收
        private DSStack<int> _recycle;

        //数据需要三个数据来存储内容，分别存储前后节点索引和数据本身
        private int[] _prev;
        private T[] _ds;
        private int[] _next;

        //链表头尾的索引，跟踪表尾主要方便LRU使用
        private int _head;
        private int _tail;

        public DSChain(int length)
        {
            _head = -1;
            _tail = -1;
            _prev = new int[length];
            _ds = new T[length];
            _next = new int[length];

            _recycle = new DSStack<int>(length);
            //将所有可用空间压入栈，也可改良当顺序空间耗尽后再读取栈中记录的回收空间
            for (int i = 0; i < length; i++)
            {
                _recycle.Push(i);
            }
        }

        //搜索数据，返回所在索引
        int Search(T data)
        {
            if (_head == -1) return -1;
            int index = _head;
            while (!_ds[index].Equals(data))
            {
                index = _next[index];
                if (index == -1) return -1;
            }
            return index;
        }

        public bool Insert(T data)
        {
            int index;
            if (!_recycle.Pop(out index)) return false;
            if (_head == -1)
            {
                _prev[index] = -1;
                _ds[index] = data;
                _next[index] = -1;
                _tail = index;
            }
            else
            {
                _prev[index] = -1;
                _ds[index] = data;
                _next[index] = _head;
                _prev[_head] = index;
            }
            _head = index;
            return true;
        }

        public bool Delete(T data)
        {
            int index = Search(data);
            if (index == -1) return false;

            if (_prev[index] != -1) _next[_prev[index]] = _next[index];
            else _head = _next[index];

            if (_next[index] != -1) _prev[_next[index]] = _prev[index];
            else _tail = _prev[index];

            _recycle.Push(index);
            return true;
        }

        //LRU
        public bool DeleteLast()
        {
            int index = _tail;
            if (index == -1) return false;
            _tail = _prev[index];
            _next[_prev[index]] = -1;
            _recycle.Push(index);
            return true;
        }

        //LRU访问方法，读取数据的同时调整数据在链表中位置
        //链表这种数据结构实现LRU非常方便
        public bool LRUAccess(T data)
        {
            int index = Search(data);
            if (index == -1) return false;
            if (_head == index) return true;
            if (_tail == index) _tail = _prev[index];

            _next[_prev[index]] = _next[index];
            if (_next[index] != -1) _prev[_next[index]] = _prev[index];

            _prev[index] = -1;
            _next[index] = _head;
            _prev[_head] = index;
            _head = index;
            return true;
        }
    }