移除元素

双指针
删除指定项且不改变顺序

def removeElement(nums: list[int], val: int) -> int:fast = slow = 0while fast < len(nums):if nums[fast] != val:nums[slow] = nums[fast]slow += 1# 当 fast 指针遇到要删除的元素时停止赋值# slow 指针停止移动, fast 指针继续前进fast += 1return slow
nums = [0,1,2,2,3,0,4,2,2,2]
val = 2
print(removeElement(nums,val))

删除有序数组中的重复项

删除重复项且不改变顺序

def removeDuplicates(nums: list[int]) -> int:slow = 0for fast in range(len(nums)):if fast == 0:nums[slow] = nums[fast]slow += 1if fast >= 1:if nums[fast] != nums[fast - 1]:nums[slow] = nums[fast]slow += 1return slownums = [1,1,2]
print(removeDuplicates(nums))

或者：

def removeDuplicates(nums: list[int]) -> int:for i in range(len(nums) - 1, 0, -1):if nums[i] == nums[i - 1]:nums.pop(i)return len(nums)nums = [0,0,1,1,1,2,2,3,3,4]
print(removeDuplicates(nums))

移动零

和题一一样操作

def moveZeroes(nums: list[int]) -> None:"""Do not return anything, modify nums in-place instead."""slow, fast = 0, 0while fast < len(nums):if nums[fast] != 0:nums[slow] = nums[fast]slow += 1fast += 1for i in range(slow,len(nums)):nums[i] = 0return numsnums = [0,1,0,3,12]
print(moveZeroes(nums))

比较含退格的字符串

想不到

def backspaceCompare(s: str, t:str) -> bool:i, j = len(s) - 1, len(t) - 1skipS, skipT = 0, 0while i >= 0 or j >= 0:# S循环while i >= 0:if s[i] == '#':skipS += 1i -= 1elif skipS > 0:skipS -= 1i -= 1else:break# T循环while j >= 0:if t[j] == '#':skipT += 1j -= 1elif skipT > 0:skipT -= 1j -= 1else:breaka = "" if i < 0 else s[i] # a[-1] = a,所以不能有负索引b = "" if j < 0 else t[j]if a != b:return Falsei -= 1j -= 1return Trues = "aaa###a"
t = "aaaa###a"
print(backspaceCompare(s,t))

有序数组的平方

正负数平方排序

def sortedSquares(nums: list[int]) -> list[int]:for i in range(len(nums)):nums[i] = nums[i] * nums[i]nums.sort()return nums
nums = [-4,-1,0,3,10]
print(sortedSquares(nums))

或者：

def sortedSquares(nums: list[int]) -> list[int]:left = 0right = len(nums) - 1temp_lis = [-1] * len(nums)site = len(nums) - 1while left <= right:if nums[left] ** 2 < nums[right] ** 2:temp_lis[site] = nums[right] ** 2right -= 1else:temp_lis[site] = nums[left] ** 2left += 1site -= 1return temp_lis
nums = [-4,-1,0,3,10]
print(sortedSquares(nums))