import heapq
from collections import Counter
class Solution1:
def topKFrequent(self, words: list[str], k: int) -> list[str]:
c = Counter(words)
return [x for x in sorted(c, key=lambda key: (-c[key], key))][:k]
class Solution:
def topKFrequent(self, words: list[str], k: int) -> list[str]:
c = Counter(words)
return heapq.nsmallest(k, c, key=lambda key: (-c[key], key))
import heapq
class Solution:
def lastStoneWeight(self, stones: list[int]) -> int:
stones.append(0)
stones = list(map(lambda x: -x, stones))
heapq.heapify(stones)
while len(stones) > 1:
y, x = -heapq.heappop(stones), -heapq.heappop(stones)
if x != y:
heapq.heappush(stones, -(y - x))
return -heapq.heappop(stones)
class Solution1:
def backspaceCompare(self, s: str, t: str) -> bool:
S = '#'
ss, st = [], []
for c in s:
if c != S:
ss.append(c)
elif ss:
ss.pop()
for c in t:
if c != S:
st.append(c)
elif st:
st.pop()
return ss == st
class Solution:
def backspaceCompare(self, s: str, t: str) -> bool:
def go_left(string, pointer, backspace):
S = '#'
while pointer >= 0 and (backspace or string[pointer] == S):
backspace += (-1) ** (string[pointer] != S)
pointer -= 1
return pointer, backspace
ps, pt = len(s) - 1, len(t) - 1 # pointer
bs, bt = 0, 0 # backspace
while True:
(ps, bs), (pt, bt) = go_left(s, ps, bs), go_left(t, pt, bt)
if not (ps >= 0 and pt >= 0 and s[ps] == t[pt]):
return ps == pt == -1
ps -= 1
pt -= 1
from collections import Counter
class Solution:
def getHint(self, s: str, g: str) -> str:
a, b = 0, 0
cs, cg = Counter(), Counter()
for i in range(len(s)):
if s[i] == g[i]:
a += 1
continue
if cg[s[i]]:
cg[s[i]] -= 1
b += 1
else:
cs[s[i]] += 1
if cs[g[i]]:
cs[g[i]] -= 1
b += 1
else:
cg[g[i]] += 1
return f'{a}A{b}B'
import math
class Solution1:
def uniquePaths(self, m: int, n: int) -> int:
return math.comb((m - 1) + (n - 1), (n - 1))
class Solution:
def uniquePaths(self, m: int, n: int) -> int:
dp = [1] + [0 for _ in range(n - 1)]
for _ in range(m):
for i in range(n - 1):
dp[i + 1] += dp[i]
return dp[n - 1]
class Solution: # O(n) / O(n)
# https://leetcode.com/problems/longest-repeating-character-replacement/solutions/278271/C++Python-Sliding-Window-O(N)-instead-of-O(26N)/
def characterReplacement(self, s: str, k: int) -> int:
c = {} # counter
mf = 0 # max_freq
i = 0
for j, char in enumerate(s):
c[char] = c.get(char, 0) + 1
mf = max(mf, c[char])
if not ((j - i + 1) - mf <= k): # shift right
c[s[i]] -= 1
i += 1
return len(s) - i # length
class Solution2: # O(n) / O(n)
# https://leetcode.com/problems/longest-repeating-character-replacement/solutions/278271/C++Python-Sliding-Window-O(N)-instead-of-O(26N)/
def characterReplacement(self, s: str, k: int) -> int:
c = {}
mf, i = 0, 0
for j, char in enumerate(s):
c[char] = c.get(char, 0) + 1
mf = max(mf, c[char])
if i - mf >= k:
c[s[j - i]] -= 1
else:
i += 1 # update when more
return i
class SolutionBS: # O(log(n)) / O(n)
# TODO: review
# https://leetcode.com/problems/longest-repeating-character-replacement/solutions/2805777
def characterReplacement(self, s: str, k: int) -> int:
def too_long(length: int):
c = {}
mf, i = 0, 0
for j, char in enumerate(s):
c[char] = c.get(char, 0) + 1
mf = max(mf, c[char])
if length - mf <= k:
return False
if j - i + 1 > length:
c[s[i]] -= 1
i += 1
return True
l, r = 0, len(s)
while l < r:
m = (l + r) // 2
l, r = (l, m) if too_long(length=m + 1) else (m + 1, r)
return (l - 1) + 1
from collections import Counter
class Solution:
def findAnagrams(self, s: str, p: str) -> list[int]:
result, s, P = [], s + ' ', len(p)
cp, cs = Counter(p), Counter(s[:P])
for i in range(len(s) - P):
if cp == cs:
result.append(i)
cs.subtract(s[i])
cs.update(s[i + P])
return result
class Solution:
def climbStairs(self, n: int) -> int:
a, b = 1, 1
for _ in range(n):
a, b = b, a + b
return a
class Solution:
def fib(self, n: int) -> int:
a, b = 0, 1
for _ in range(n):
a, b = b, a + b
return a
class Solution:
def minCostClimbingStairs(self, cost: list[int]) -> int:
a = b = 0
for c in cost:
a, b = b, min(a, b) + c
return min(a, b)
class Solution:
def numIslands(self, grid) -> int:
M, N = len(grid), len(grid[0])
def dfs(m, n):
r = 0 <= m < M and 0 <= n < N and grid[m][n] == '1'
if r:
grid[m][n] = None
list(map(dfs, (m + 1, m - 1, m, m), (n, n, n + 1, n - 1)))
return r
return sum(dfs(m, n) for m in range(M) for n in range(N))
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def lowestCommonAncestor(self, root, p, q):
if root.val > max(p.val, q.val):
return self.lowestCommonAncestor(root.left, p, q)
if root.val < min(p.val, q.val):
return self.lowestCommonAncestor(root.right, p, q)
return root
class Solution:
def floodFill(
self, image: list[list[int]], sr: int, sc: int, color: int
) -> list[list[int]]:
COLOR, M, N = image[sr][sc], len(image), len(image[0])
def dfs(m, n):
if not all([0 <= m < M, 0 <= n < N]):
return
if not all([image[m][n] == COLOR, image[m][n] != color]):
return
image[m][n] = color
list(map(dfs, (m + 1, m - 1, m, m), (n, n, n + 1, n - 1)))
dfs(sr, sc)
return image
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def isValidBST(self, root, lo=float('-inf'), hi=float('inf')) -> bool:
'''
[5,4,6,null,null,3,7] => false
'''
return (not root) or all(
[
lo < root.val < hi,
self.isValidBST(root.left, lo, root.val),
self.isValidBST(root.right, root.val, hi),
]
)
from functools import reduce
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def levelOrder(self, root) -> list[list[int]]:
result, q = [], [root]
while True:
q = [x for x in q if x]
v = [x.val for x in q]
if not v:
break
result.append(v)
q = reduce(lambda a, b: a + [b.left, b.right], q, [])
return result
class Solution:
def search(self, nums: list[int], target: int) -> int:
l, r = 0, len(nums)
while l < r:
m = (l + r) // 2
if nums[m] == target:
return m
l, r = (l, m) if nums[m] > target else (m + 1, r)
return -1
class Solution:
def maxProfit(self, prices) -> int:
result, buy = 0, prices[0]
for p in prices:
result, buy = max(result, p - buy), min(buy, p)
return result
class Solution:
def detectCycle(self, head):
'''
.___a___.___C-b___.
(_________) -> C: cycle
b
slow: a+C-b + xC
fast: a+C-b + yC
2 slow = fast
=> a+C-b = (y-2x)C
=> a = (y-2x-1)C+b
.___(y-2x-1)C+b___.___C-b___.
(_________)
b
=> a mod C = b mod C
'''
l = r = head
while r and r.next:
l, r = l.next, r.next.next
if l is r:
break
else:
return
while head is not r:
head, r = head.next, r.next
return head
class Solution:
def longestPalindrome(self, s: str) -> int:
r, pool = 0, set()
for c in s:
if c in pool:
pool.remove(c)
r += 1
else:
pool.add(c)
return r * 2 + bool(pool)
class Node:
def __init__(self, val=None, children=None):
self.val = val
self.children = children
class Solution:
def preorder(self, root):
return (
(root.val,) + sum((self.preorder(x) for x in root.children), ())
if root
else ()
)