力扣LFU460

好难的460

比146还难。看了两遍视频解答，看懂一点点。而且一些大厂好像还喜欢面试问！

# problemkey 就是跟LRU不一样的是，LRU去掉最久没用的，LFU去掉用频率最小的
class Node:
    def __init__(self, key, val, pre=None, nex=None, freq=0):
        self.pre = pre
        self.nex = nex
        self.freq = freq
        self.val = val
        self.key = key

    def insert(self, nex):
        nex.pre = self
        nex.nex = self.nex
        self.nex.pre = nex
        self.nex = nex


def create_linked_list():
    head = Node(float('inf'), float('inf'))
    tail = Node(float('inf'), float('inf'))
    head.nex = tail
    tail.pre = head
    return (head, tail)


class LFUCache_LC:
    def __init__(self, capacity: int):
        self.capacity = capacity
        self.size = 0
        self.minFreq = 0
        self.freqMap = collections.defaultdict(create_linked_list)
        self.keyMap = {}

    # 把node删掉，可能是因为淘汰了，也可能是频率增加要换位置
    def delete(self, node):
        if node.pre:
            node.pre.nex = node.nex
            node.nex.pre = node.pre
            if node.pre is self.freqMap[node.freq][0] and node.nex is self.freqMap[node.freq][-1]:
                self.freqMap.pop(node.freq)
        return node.key
    # freq 加一个，get一次就得加一次频率
    def increase(self, node):
        node.freq += 1
        self.delete(node)
        self.freqMap[node.freq][-1].pre.insert(node)
        if node.freq == 1:
            self.minFreq = 1
        elif self.minFreq == node.freq - 1:
            head, tail = self.freqMap[node.freq - 1]
            if head.nex is tail:
                self.minFreq = node.freq

    def get(self, key: int) -> int:
        if key in self.keyMap:
            self.increase(self.keyMap[key])
            return self.keyMap[key].val
        return -1

    def put(self, key: int, value: int) -> None:
        if self.capacity != 0: # 这个东西都不变啊，就是一开始设置0的话，不用put
            if key in self.keyMap:
                node = self.keyMap[key]
                node.val = value
            else:
                node = Node(key, value)
                self.keyMap[key] = node
                self.size += 1
            if self.size > self.capacity:
                self.size -= 1
                deleted = self.delete(self.freqMap[self.minFreq][0].nex)
                self.keyMap.pop(deleted)
            self.increase(node)