边工作边刷题：70天一遍leetcode: day 8-2

LRU Cache

这题调了好几天才pass
要点：用doubly linked list，

• deleteNode和addNode分开考虑，分开考虑，分开考虑，重要的事情说三遍
• 需要dummy node和tail，deleteNode考虑tail，addNode考虑dummy.next（因为addNode alway加头）
• set()：最外分支是是否key已经在map里（在表示update），没在always加头

错误点：

• 空间满了以后先size--，这样空间未满的情况统一处理，注意别忘了size++
• remove key from hmap顺序反了，固化：永远在改变结点之前。
• 这题错误大多在deleteNode和addNode里，而且很难debug，比如，忘了连接dummy.next

class LRUCache(object):
    class ListNode(object):
        def __init__(self, key, val):
            self.key = key
            self.val = val
            self.next = None
            self.prev = None
    
    def __init__(self, capacity):
        """
        :type capacity: int
        """
        self.capacity = capacity
        self.size = 0
        self.hmap = {}
        self.dummy = self.ListNode(0,0)
        self.tail = self.dummy

    def get(self, key):
        """
        :rtype: int
        """
        hmap=self.hmap
        if key not in hmap:
            return -1
            
        val = hmap[key].val
        self.deleteNode(hmap[key])
        self.addNode(hmap[key])
        return val

    def set(self, key, value):
        """
        :type key: int
        :type value: int
        :rtype: nothing
        """
        hmap=self.hmap
        if key not in hmap:
            print self.size,self.capacity
            if self.size==self.capacity:
                print self.tail.key
                hmap.pop(self.tail.key)
                self.deleteNode(self.tail)
                self.size-=1
            hmap[key]=self.ListNode(key,value)
            self.addNode(hmap[key])
            self.size+=1
        else:
            hmap[key].val=value
            self.deleteNode(hmap[key])
            self.addNode(hmap[key])
        
    def deleteNode(self, node):
        # print self.hmap, node.val, self.tail.val
        if self.tail==node:
            self.tail = self.tail.prev
            self.tail.next = None
        else:
            node.prev.next = node.next
            node.next.prev = node.prev
        
    def addNode(self, node):
        dummy = self.dummy
        if dummy.next:
            dummy.next.prev = node
        else:
            self.tail = node
        node.prev = dummy
        node.next = dummy.next
        dummy.next = node