Python 实例教程

  • Python 实例教学_ 06_集合
  • 第二十八课
  • 888. 公平的糖果棒交换
  • [2351. 第一个出现两次的字母](https://leetcode.cn/problems/first-letter-to-appear-twice/)
  • [217. 存在重复元素](https://leetcode.cn/problems/contains-duplicate/)
  • [219. 存在重复元素 II](https://leetcode-cn.com/problems/contains-duplicate-ii/)
  • 第二十九课
  • [268. 丢失的数字](https://leetcode.cn/problems/missing-number/)
  • [929. 独特的电子邮件地址](https://leetcode.cn/problems/unique-email-addresses/)
  • [2215. 找出两数组的不同](https://leetcode.cn/problems/find-the-difference-of-two-arrays/)
  • 第三十课
  • [575. 分糖果](https://leetcode.cn/problems/distribute-candies/)
  • ★575. 分糖果
  • [1684. 统计一致字符串的数目](https://leetcode.cn/problems/count-the-number-of-consistent-strings/)
  • [2460. 对数组执行操作](https://leetcode.cn/problems/apply-operations-to-an-array/)
  • [1710. 卡车上的最大单元数](https://leetcode.cn/problems/maximum-units-on-a-truck/)


Python 实例教学_ 06_集合

Python 1-19 集合

第二十八课

888. 公平的糖果棒交换

Leetcode知识点： sum set 总体差的一半通过交换重新分配

class Solution:
    def fairCandySwap(self, aliceSizes: List[int], bobSizes: List[int]) -> List[int]:
        a, b = sum(aliceSizes), sum(bobSizes)
        c, d = aliceSizes, set(bobSizes)
        for i in c:                    
            j = (b - a)//2 + i
            if j in d:
                return [i, j]

2351. 第一个出现两次的字母 

class Solution:
    def repeatedCharacter(self, s: str) -> str:
        st = set()
        for c in s:
            if c in st: return c
            st.add(c)

217. 存在重复元素 

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        d = defaultdict(int)
        for x in nums:
            if x in d:
                return True
            d[x] += 1
        return False

        s = set()
        for x in nums:
            if x in s:
                return True
            s.add(x)
        return False

        return len(set(nums)) != len(nums)

219. 存在重复元素 II 

class Solution:
    def containsNearbyDuplicate(self, nums: List[int], k: int) -> bool:
        
        # 1、双 for 超时
        # n = len(nums)
        # for i in range(n):
        #     for j in range(i + 1, n):
        #         if nums[i] == nums[j] and j - i <= k:
        #             return True
        # return False

        # 2、dict
        d = defaultdict(int)
        for i, x in enumerate(nums):
            if x in d and i - d[x] <= k: return True
            d[x] = i
        return False

        # 3、set
        s, left = set(), 0
        # for i, x in enumerate(nums):
        for x in nums:
            if x in s: return True
            s.add(x)
            # if len(s) > k: s.remove(nums[i - k])
            if len(s) > k: 
            	s.remove(nums[left])
            	left += 1           
        return False

第二十九课

268. 丢失的数字 

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        ## 方法一：排序
        # n = len(nums)
        # nums.sort()
        # for i in range(n):
        #     if nums[i] != i:
        #         return i
        # return n

        ## 方法二：哈希表
        # hash = set(nums)
        # for i in range(len(nums) + 1):
        #     if i not in hash:
        #         return i

        ## 方法三：差
        # return sum(range(len(nums) + 1)) - sum(nums)
        # return (n := len(nums)) * (n + 1) // 2 - sum(nums)

        ## 方法四：异或
        res = 0
        for i, num in enumerate(nums):
            res ^= i ^ num

        res ^= len(nums)

        return res

929. 独特的电子邮件地址 

class Solution:
    def numUniqueEmails(self, emails: List[str]) -> int:
        emailSet = set()
        for email in emails:
            i = email.index('@')
            local = email[:i].split('+', 1)[0]  # 去掉本地名第一个加号之后的部分
            local = local.replace('.', '')  # 去掉本地名中所有的句点
            emailSet.add(local + email[i:])
        return len(emailSet)

2215. 找出两数组的不同 

class Solution:
    def findDifference(self, nums1: List[int], nums2: List[int]) -> List[List[int]]:
        a, b = set(nums1), set(nums2)
        
        return [list(a - b), list(b - a)]

第三十课

575. 分糖果 

class Solution:
    def distributeCandies(self, candyType: List[int]) -> int:
        n = len(candyType) // 2
        s = set(candyType)
        if len(s) >= n: return n
        return len(s)
        
        # return min(len(candyType)//2, len(set(candyType)))

★575. 分糖果

Leetcode知识点： 集合 set set.add，去重功能，无序，分类。// 整除、/ 除法。

class Solution:
    def distributeCandies(self, candyType: List[int]) -> int:        
        n = len(candyType)//2
        s = set()
        for c in candyType:
            s.add(c)        
        return len(s) if len(s) <= n else n
        
        #return min(len(candyType)//2, len(set(candyType)))

1684. 统计一致字符串的数目 

class Solution:
    def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
        res = 0
        for w in words: # 外循环
            # flag = True
            # for c in w: # 内循环
            #     if c not in allowed:
            #         flag = False
            #         break # 终止（内）循环
            # if flag: res += 1

            # for c in w: # 内循环
            #     if c not in allowed:                    
            #         break # 终止（内）循环
            # else: res += 1 # 这个是和 for 对齐的，跳过 break 终止的循环

            res += all(c in allowed for c in w)
        return res

        return sum(all(c in allowed for c in w) for w in words)
        return sum(set(allowed) >= set(s) for s in words)

2460. 对数组执行操作 

class Solution:
    def applyOperations(self, nums: List[int]) -> List[int]:
        n, left = len(nums), 0
        for i in range(n):
            if i + 1 < n and nums[i] == nums[i + 1]:
                nums[i], nums[i + 1] = nums[i] * 2, 0
            if nums[i]:
                nums[i], nums[left] = nums[left], nums[i]
                left += 1
        return nums

1710. 卡车上的最大单元数 

class Solution:
    def maximumUnits(self, boxTypes: List[List[int]], truckSize: int) -> int:
        boxTypes.sort(key=lambda x:-x[1])
        ans = 0
        for a, b in boxTypes:
            if a >= truckSize:
                ans += truckSize * b
                break            
            ans += a * b
            truckSize -= a            
        return ans