存在重复元素
"""
思路：列表转为集合，判断集合长度和列表长度是否相等，相等False，否则True
"""
class Solution:
def containsDuplicate(self, nums: List[int]) -> bool:
if len(set(nums)) == len(nums):
return False
return True只出现一次的数字
"""
思路：`nums.count(i)` 计算出现次数
"""
class Solution:
def singleNumber(self, nums: List[int]) -> int:
for i in nums:
if nums.count(i) == 1:
return i两个数组的交集
"""
思路： 先排序，然后根据索引判断对应位置数字是否相等，相等加入到空列表中，不想等数字小的i+1继续比较
"""
class Solution:
def intersect(self, nums1: List[int], nums2: List[int]) -> List[int]:
nums1.sort()
nums2.sort()
i = j = 0
lst = []
while i<len(nums1) and j<len(nums2):
if nums1[i] == nums2[j]:
lst.append(nums1[i])
i += 1
j += 1
elif nums1[i] < nums2[j]:
i += 1
else:
j += 1
return lst加一
"""
思路： 递归。先判断数组是否为空，再判断最后一位是否为9，等于9递归调用到[:-1]，不等于9最后一位+1
"""
class Solution:
def plusOne(self, digits: List[int]) -> List[int]:
if len(digits) == 0:
digits = [1]
elif digits[-1] == 9:
digits = self.plusOne(digits[:-1])
digits.extend([0])
else:
digits[-1] += 1
return digits移动零
"""
思路：先计算数组中0的个数，根据个数删除数组中的零，最后再数组最后添加相应个数的0
"""
class Solution:
def moveZeroes(self, nums: List[int]) -> None:
"""
Do not return anything, modify nums in-place instead.
"""
count = nums.count(0)
for i in range(count):
nums.remove(0)
nums.extend([0]*count)
return nums两数之和
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
if nums == None or len(nums) < 2:
return None
res_dict = {}
for i, item in enumerate(nums):
if (target - item) in res_dict.keys():
return (res_dict[target - item], i)
else:
res_dict[item] = i
return (-1, -1)旋转图像
class Solution:
# 方法一：矩阵转置
def rotate(self, matrix: List[List[int]]) -> None:
"""
Do not return anything, modify matrix in-place instead.
"""
n = len(matrix)
# 矩阵反转
for i in range(n):
for j in range(i, n):
matrix[j][i], matrix[i][j] = matrix[i][j], matrix[j][i]
for i in range(n):
matrix[i].reverse()
# 方法二：zip()函数
def rotate1(self, matrix: List[List[int]]) -> None:
"""
Do not return anything, modify matrix in-place instead.
"""
matrix[:] = zip(*matrix[::-1])有效的数独
class Solution:
def isValidSudoku(self, board: List[List[str]]) -> bool:
row = [[] for _ in range(9)]
col = [[] for _ in range(9)]
cell = [[] for _ in range(9)]
for i, item in enumerate(board):
for j, num in enumerate(item):
if num != '.':
k = i//3*3 + j//3
if num in row[i] + col[j] + cell[k]:
return False
row[i].append(num)
col[j].append(num)
cell[k].append(num)
return True
