Question 146: LRU Caching Mechanism
Use the data structure you know to design and implement an LRU (least recently used) caching mechanism.
Implement the LRUCache class:
LRUCache(int capacity) Initialize the LRU cache with a positive integer as capacity capacity
int get(int key) If the keyword key exists in the cache, return the value of the keyword, otherwise return -1.
void put(int key, int value) If the keyword already exists, change its data value; if the keyword does not exist, insert the set of "keyword-value". When the cache capacity reaches the upper limit, it should delete the oldest unused data value before writing new data to make room for the new data value.
answer:
class LRUCache:
def __init__(self, capacity: int):
self.capacity = capacity
self.cache = {
}
def get(self, key: int) -> int:
if key not in self.cache:
return -1
self.cache[key] = self.cache.pop(key)
return self.cache[key]
def put(self, key: int, value: int) -> None:
if key in self.cache:
self.cache.pop(key)
self.cache[key] = value
if len(self.cache) > self.capacity:
x = list(self.cache)[0]
self.cache.pop(x)
Operation result:
Question 148: Sorting Linked List
Give you the head node head of the linked list, please sort it in ascending order and return to the sorted linked list.
answer:
class Solution:
def sortList(self, head: ListNode) -> ListNode:
nodes = []
while head:
nodes.append(head)
head = head.next
nodes = sorted(nodes, key = lambda x: x.val)
cur = head = ListNode()
for i in range(len(nodes)):
cur.next = nodes[i]
cur = cur.next
cur.next = None
return head.next
Running result:
Topic 155: Minimal stack
Design a stack that supports push, pop, and top operations, and can retrieve the smallest element in a constant time.
push(x)-Push element x onto the stack.
pop() —— Delete the element at the top of the stack.
top()-Get the top element of the stack.
getMin()-Retrieve the smallest element in the stack.
answer:
class MinStack:
def __init__(self):
self._list = []
def push(self, x: int) -> None:
self._list.append(x)
self._min = min(self._list)
def pop(self) -> None:
self._list.pop()
self._min = not self._list or min(self._list)
def top(self) -> int:
return self._list[-1]
def getMin(self) -> int:
return self._min
operation result:
