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assignment4.py
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assignment4.py
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from collections import defaultdict, Counter, deque
from heapq import heappush, heappop, heapreplace, heapify
import math
class Node:
def __init__(self, k, v):
"""
:type k: int
:type v: int
"""
self.key = k
self.val = v
self.prev = None
self.next = None
class LRUCache(object):
def __init__(self, capacity):
"""
:type capacity: int
"""
self.capacity = capacity
self.dic = dict()
self.head = Node(None, None)
self.tail = Node(None, None)
self.head.next = self.tail
self.tail.prev = self.head
def get(self, key):
"""
:type key: int
:rtype: int
"""
if key in self.dic: # if the key exists
n = self.dic[key] # get the node
self.removeNode(n) # remove it from the linked list
self.addNode(n) # readd it since it's now the most recent
return n.val
return -1
def put(self, key, value):
"""
:type key: int
:type value: int
:rtype: None
"""
if key in self.dic: # if the key exists
self.removeNode(self.dic[key]) # remove it from the linkedlist
n = Node(key, value)
self.addNode(n) # add new Node to linked list
self.dic[key] = n # add it to the dictionary
if len(self.dic) > self.capacity: # if cache/linked list is at capacity
n = self.head.next # remove the head (the oldest node)
self.removeNode(n)
del self.dic[n.key] # delete it from the dictionary
def removeNode(self, node):
"""
:type node: Node
"""
p = node.prev
n = node.next
p.next = n
n.prev = p
def addNode(self, node):
"""
:type node: Node
"""
p = self.tail.prev
p.next = node
self.tail.prev = node
node.prev = p
node.next = self.tail
class MyStack(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.deque = deque()
def push(self, x):
"""
Push element x onto stack.
:type x: int
:rtype: None
"""
self.deque.append(x)
def pop(self):
"""
Removes the element on top of the stack and returns that element.
:rtype: int
"""
return self.deque.pop()
def top(self):
"""
Get the top element.
:rtype: int
"""
return self.deque[-1]
def empty(self):
"""
Returns whether the stack is empty.
:rtype: bool
"""
return not self.deque
class MyQueue(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.deque = deque()
def push(self, x):
"""
Push element x to the back of queue.
:type x: int
:rtype: None
"""
self.deque.append(x)
def pop(self):
"""
Removes the element from in front of queue and returns that element.
:rtype: int
"""
return self.deque.popleft()
def peek(self):
"""
Get the front element.
:rtype: int
"""
return self.deque[0]
def empty(self):
"""
Returns whether the queue is empty.
:rtype: bool
"""
return not self.deque
class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
prev = None
while head != None:
curr = head
head = head.next
curr.next = prev
prev = curr
return prev
def reverseBetween(self, head, m, n):
"""
:type head: ListNode
:type m: int
:type n: int
:rtype: ListNode
"""
dummy = ListNode(0)
dummy.next = head
curr = head
prev = dummy
for x in range(m - 1):
curr = curr.next
prev = prev.next
for x in range(n-m):
temp = curr.next
curr.next = temp.next
temp.next = prev.next
prev.next = temp
return dummy.next
def oddEvenList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if head == None or head.next == None:
return head
odd = head
even = head.next
evenHead = even
while even != None and even.next != None:
odd.next = odd.next.next
odd = odd.next
even.next = even.next.next
even = even.next
odd.next = evenHead
return head
def getIntersectionNode(self, headA, headB):
"""
:type head1, head1: ListNode
:rtype: ListNode
"""
if headA and headB:
A = headA
B = headB
while A != B:
if A:
A = A.next
elif not A:
A = headB
if B:
B = B.next
elif not B:
B = headA
return A
def reverseKGroup(self, head, k):
"""
:type head: ListNode
:type k: int
:rtype: ListNode
"""
jump = ListNode(-1)
dummy = jump
dummy.next = head
l = head
r = head
while True:
count = 0
while r and count < k:
count += 1
r = r.next
if count == k:
prev = r
curr = l
for x in range(k):
temp = curr.next
curr.next = prev
prev = curr
curr = temp
jump.next = prev
jump = l
l = r
else:
return dummy.next
def calPoints(self, ops):
"""
:type ops: List[str]
:rtype: int
"""
stack = []
for i in range(len(ops)):
if ops[i] == "C":
stack.pop()
elif ops[i] == "D":
stack.append(stack[-1]*2)
elif ops[i] == "+":
stack.append(stack[-1]+stack[-2])
else:
stack.append(int(ops[i]))
return sum(stack)
def nextGreaterElement(self, nums1, nums2):
"""
:type nums1: List[int]
:type nums2: List[int]
:rtype: List[int]
"""
dic = {}
stack = []
for x in nums2:
while stack and stack[-1] < x:
dic[stack.pop()] = x
stack.append(x)
result = [-1]*len(nums1)
for i,x in enumerate(nums1):
if x in dic:
result[i] = dic[x]
return result
def backspaceCompare(self, S, T):
"""
:type S: str
:type T: str
:rtype: bool
"""
back = lambda res, c: res[:-1] if c == '#' else res + c
return reduce(back, S, "") == reduce(back, T, "")
def isValid(self, s):
"""
:type s: str
:rtype: bool
"""
stack = []
dic = {"]":"[", "}":"{", ")":"("}
for c in s:
if c in dic.values():
stack.append(c)
elif c in dic.keys():
if stack == [] or dic[c] != stack.pop():
return False
else:
return False
return stack == []
def scoreOfParentheses(self, S):
"""
:type S: str
:rtype: int
"""
stack = [0]
for c in S:
if c == "(":
stack.append(0)
else:
last = stack.pop()
stack[-1] += max(2*last, 1)
return stack.pop()
def rotate(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: None Do not return anything, modify nums in-place instead.
"""
n = len(nums)
k = k % n
j = 0
while n > 0 and k % n != 0:
for i in range(0, k):
nums[j+i], nums[len(nums)-k+i] = nums[len(nums)-k+i], nums[j+i]
n = n-k
j = j+k
k = k % n
def topKFrequent(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: List[int]
"""
freq = []
counter = Counter(nums)
# since it will be a min heap but we want the most frequent we switch them to negative
h = [(-count, num) for num, count in counter.items()]
heapify(h)
while len(freq) < k:
freq.append(heappop(h)[1])
return freq
def mergeKLists(self, lists):
"""
:type lists: List[ListNode]
:rtype: ListNode
"""
node = ListNode(None)
dummy = node
h = [(n.val, n) for n in lists if n] # list of head nodes
heapify(h)
while h:
v, n = h[0] # get the min in the heap, the value and the head
if n.next is None:
heappop(h) # None means end of list we're on, ignore it
else:
heapreplace(h, (n.next.val, n.next)) # pop min node and push the min node's next
node.next = n # linking each min node so it's sorted
node = node.next
return dummy.next
def subsets(self, nums):
"""
:type nums: List[int]
:rtype: List[List[int]]
"""
result = [[]]
for num in nums:
result += [i + [num] for i in result]
return result
def permute(self, nums):
"""
:type nums: List[int]
:rtype: List[List[int]]
"""
return reduce(lambda P, n: [p[:i]+[n]+p[i:] for p in P for i in range(len(p)+1)], nums, [[]])
def combine(self, n, k):
"""
:type n: int
:type k: int
:rtype: List[List[int]]
"""
combs = [[]]
for x in range(k):
combs = [[i]+c for c in combs for i in range(1, c[0] if c else n+1)]
return combs
def generateParenthesis(self, n):
"""
:type n: int
:rtype: List[str]
"""
dp = [[] for i in range(n+1)]
dp[0].append('')
for i in range(n+1):
for j in range(i):
dp[i] += ['('+x+')'+y for x in dp[j] for y in dp[i-j-1]]
return dp[n]
def grayCode(self, n):
"""
:type n: int
:rtype: List[int]
"""
res = [0]
for i in range(n):
for j in range(len(res)-1, -1, -1):
res.append(res[j] | 1<<i)
return res
def allPossibleFBT(self, N):
"""
:type N: int
:rtype: List[TreeNode]
"""
N -= 1
if N == 0: return [TreeNode(0)]
ret = []
for l in range(1, N, 2):
for left in self.allPossibleFBT(l):
for right in self.allPossibleFBT(N - l):
root = TreeNode(0)
root.left = left
root.right = right
ret += [root]
return ret
def combinationSum(self, candidates, target):
"""
:type candidates: List[int]
:type target: int
:rtype: List[List[int]]
"""
res = []
self.dfsCombSum(candidates, target, 0, [], res)
return res
def dfsCombSum(self, candidates, target, index, path, res):
if target < 0:
return res
if target == 0:
res.append(path)
return res
for i in range(index, len(candidates)):
self.dfsCombSum(candidates, target-candidates[i], i, path+[candidates[i]], res)
def canPartition(self, nums):
"""
:type nums: List[int]
:rtype: bool
"""
total = 0
for num in nums:
total += num
if (total%2) == 1:
return False
half = total/2
n = len(nums)
dp = [False] * (half+1)
dp[0] = True
for num in nums:
i = half
while i > 0:
if i >= num:
dp[i] = dp[i] or dp[i-num]
i -= 1
return dp[half]
def canPartitionKSubsets(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: bool
"""
nums.sort(reverse=True)
parts = [0] * k
kSum = sum(nums) // k
return self.dfsKSubsets(0, nums, k, parts, kSum)
def dfsKSubsets(self, ind, nums, k, parts, kSum):
if ind == len(nums):
return True
for i in range(k):
parts[i] += nums[ind]
if parts[i] <= kSum and self.dfsKSubsets(ind+1, nums, k, parts, kSum):
return True
parts[i] -= nums[ind]
if parts[i] == 0:
break
return False
def solveSudoku(self, board):
"""
:type board: List[List[str]]
:rtype: None Do not return anything, modify board in-place instead.
"""
self.solveFromCell(0, 0, board)
def solveFromCell(self, row, col, board):
if col == len(board[row]):
col = 0
row += 1
if row == len(board):
return True
if board[row][col] != '.':
return self.solveFromCell(row, col+1, board)
for value in range(1,len(board)+1):
val = str(value)
if self.canPlaceVal(board, row, col, val):
board[row][col] = val
if self.solveFromCell(row, col+1, board):
return True
board[row][col] = '.'
return False
def canPlaceVal(self, board, row, col, val):
for r in board:
if val == r[col]:
return False
for i in range(len(board[row])):
if val == board[row][i]:
return False
boxSize = int(math.sqrt(len(board)))
topLeftBoxRow = boxSize * (row/boxSize)
topLeftBoxCol = boxSize * (col/boxSize)
for i in range(boxSize):
for j in range(boxSize):
if val == board[topLeftBoxRow+i][topLeftBoxCol+j]:
return False
return True