Python 编程之网上刷题

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这里我们用网上评测系统来做做题。英文好的话，可以用Codeforces和LeetCode。中文可以上计蒜客和力扣。这里用LeetCode。我这里做了10道题。同时最后1题采用了多种方法，把程序效率从击败10%的提交优化到了击败99%。

1480. Running Sum of 1d Array

Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).

Return the running sum of nums.

class Solution:
    def runningSum(self, nums: [int]) -> [int]:         
      running = []
      s = 0
      for num in nums:
        s += num
        running.append(s)
      
      return running

#print(Solution().runningSum([1,2,3,4]))

第一题通过。

1108. Defanging an IP Address

Given a valid (IPv4) IP address, return a defanged version of that IP address.

A defanged IP address replaces every period "." with "[.]".

class Solution:
    def defangIPaddr(self, address: str) -> str:
        return address.replace('.', '[.]')

# print(Solution().defangIPaddr('1.1.1.1'))

1431. Kids With the Greatest Number of Candies

Given the array candies and the integer extraCandies, where candies[i] represents the number of candies that the *ith* kid has.

For each kid check if there is a way to distribute extraCandies among the kids such that he or she can have the greatest number of candies among them. Notice that multiple kids can have the greatest number of candies.

class Solution:
    def kidsWithCandies(self, candies: [int], extraCandies: int) -> [bool]:
        max = 0
        for candy in candies:
          if candy > max:
            max = candy
        greatests = []
        for candy in candies:
          if candy + extraCandies >= max:
            greatests.append(True)
          else:
            greatests.append(False)
        return greatests

# print(Solution().kidsWithCandies([2,3,5,1,3], 3))

1672. Richest Customer Wealth

You are given an m x n integer grid accounts where accounts[i][j] is the amount of money the ith customer has in the jth bank. Return the wealth that the richest customer has.

A customer’s wealth is the amount of money they have in all their bank accounts. The richest customer is the customer that has the maximum wealth.

class Solution:
    def maximumWealth(self, accounts: [[int]]) -> int:
        max = 0      
        for account in accounts:
          s = sum(account) 
          if max < s:
            max = s
        return max

#print(Solution().maximumWealth([[1,2,3],[3,2,1]]))          

1470. Shuffle the Array

Given the array nums consisting of 2n elements in the form [x1,x2,...,xn,y1,y2,...,yn].

Return the array in the form [x1,y1,x2,y2,...,xn,yn].

class Solution:
  def shuffle(self, nums: [int], n: int) -> [int]:
    ns1 = nums[:n]
    ns2 = nums[n:]
    ns = []
    for i in range(n):
      ns.append(ns1[i])
      ns.append(ns2[i])
    return ns

# print(Solution().shuffle([2,5,1,3,4,7], 3))

1512. Number of Good Pairs

Given an array of integers nums.

A pair (i,j) is called good if nums[i] == nums[j] and i< j.

Return the number of good pairs.

class Solution:
    def numIdenticalPairs(self, nums: [int]) -> int:
        j = 1
        n = len(nums)
        p = 0
        while j < n:
          for i in range(j):
            if nums[i] == nums[j]:
              p += 1
          j+=1
        return p

# print(Solution().numIdenticalPairs([1,2,3,1,1,3]))

771. Jewels and Stones

You’re given strings jewels representing the types of stones that are jewels, and stones representing the stones you have. Each character in stones is a type of stone you have. You want to know how many of the stones you have are also jewels.

Letters are case sensitive, so "a" is considered a different type of stone from "A".

class Solution:
    def numJewelsInStones(self, jewels: str, stones: str) -> int:
        n = 0
        for i in range(len(jewels)):
          js = jewels[i:i+1]
          n += stones.count(js)
        return n

# print(Solution().numJewelsInStones("aA", "aAAbbbb"))

1603. Design Parking System

Design a parking system for a parking lot. The parking lot has three kinds of parking spaces: big, medium, and small, with a fixed number of slots for each size.

Implement the ParkingSystem class:

• ParkingSystem(int big, int medium, int small)Initializes object of the ParkingSystem class. The number of slots for each parking space are given as part of the constructor.
• bool addCar(int carType) Checks whether there is a parking space of carType for the car that wants to get into the parking lot. carType can be of three kinds: big, medium, or small, which are represented by 1, 2, and 3 respectively. A car can only park in a parking space of its carType. If there is no space available, return false, else park the car in that size space and return true.

class ParkingSystem:
    slots = [0, 0, 0]

    def __init__(self, big: int, medium: int, small: int):
      self.slots[0] = big
      self.slots[1] = medium
      self.slots[2] = small        

    def addCar(self, carType: int) -> bool:
      if self.slots[carType - 1] > 0:
        self.slots[carType - 1] -=1
        return True
      else:
        return False

# parkingSystem = ParkingSystem(1, 1, 0)
# print(parkingSystem.addCar(1))
# print(parkingSystem.addCar(2))
# print(parkingSystem.addCar(3))
# print(parkingSystem.addCar(1))

1773. Count Items Matching a Rule

You are given an array items, where each items[i] = [typei, colori, namei] describes the type, color, and name of the ith item. You are also given a rule represented by two strings, ruleKey and ruleValue.

The ith item is said to match the rule if one of the following is true:

• ruleKey == "type" and ruleValue == typei.
• ruleKey == "color" and ruleValue == colori.
• ruleKey == "name" and ruleValue == namei.

Return the number of items that match the given rule.

class Solution:
    def countMatches(self, items: [[str]], ruleKey: str, ruleValue: str) -> int:
      i = 0
      if ruleKey == "type":
        i = 0
      elif ruleKey == "color":
        i = 1
      else:
        i = 2
      n = 0
      for item in items:
        if item[i] == ruleValue:
          n +=1
      return n

# print(Solution().countMatches([["phone","blue","pixel"],["computer","silver","lenovo"],["phone","gold","iphone"]], "color", "silver"))
        

1365. How Many Numbers Are Smaller Than the Current Number

Given the array nums, for each nums[i] find out how many numbers in the array are smaller than it. That is, for each nums[i] you have to count the number of valid j's such that j != i and nums[j] < nums[i].

Return the answer in an array.

Input: nums = [8,1,2,2,3]
Output: [4,0,1,1,3]
Explanation: 
For nums[0]=8 there exist four smaller numbers than it (1, 2, 2 and 3). 
For nums[1]=1 does not exist any smaller number than it.
For nums[2]=2 there exist one smaller number than it (1). 
For nums[3]=2 there exist one smaller number than it (1). 
For nums[4]=3 there exist three smaller numbers than it (1, 2 and 2).

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
        ns = []
        l = len(nums)
        for i in range(l):
          n = 0
          for j in range(l):
            if i != j:
              if nums[j] < nums[i]:
                n += 1
          ns.append(n)
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

用时528ms，击败了11.81%的程序。优化一下。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
        l = len(nums)

        sort_nums = nums.copy()

        ins = list(range(l))
        for i in range(l):          
          for j in range(i+1, l):
            if sort_nums[i] > sort_nums[j]:
              a = sort_nums[i]
              sort_nums[i] = sort_nums[j]
              sort_nums[j] = a
              
              a = ins[i]
              ins[i] = ins[j]
              ins[j] = a
        
        smalls = [0]
        for i in range(1, l):
          if sort_nums[i-1] == sort_nums[i]:
            smalls.append(smalls[i-1])
          else:
            smalls.append(i)

        # print(sort_nums)
        # print(smalls)

        r_is = list(range(l))
        for i in ins:
          r_is[ins[i]] = i
    
        ns = []
        for i in range(l):          
          ns.append(smalls[r_is[i]])
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

这会测试用时284ms，比刚刚用时528ms少。

用写系统的函数简写一下。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
        sort_nums = nums.copy()
        sort_nums.sort()
        
        ns = []
        for num in nums:
          ns.append(sort_nums.index(num))
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

这会只需用时64ms，击败了71%的提交。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
        l = len(nums)
        ns = [0] * l
        for i in range(l):
          for j in range(i+1, l):
            if nums[i] > nums[j]:
              ns[i] +=1
            elif nums[i] < nums[j]:
              ns[j] +=1
            else:
              pass
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

又想出来一种解法。用时400ms。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:        
        ss = sorted((e,i) for i,e in enumerate(nums))

        l = len(nums)
        smalls = [0]
        for i in range(1, l):
          (e0, j0) = ss[i-1]
          (e1, j1) = ss[i]
          if e0 == e1:
            smalls.append(smalls[i-1])
          else:
            smalls.append(i)

        ns = [0]*l
        for i in range(l):
          (e,j) = ss[i]
          ns[j] = smalls[i]
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

Runtime: 52 ms, faster than 91.45% of Python3 online submissions forHow Many Numbers Are Smaller Than the Current Number.

Memory Usage: 14.6 MB, less than 15.18% of Python3 online submissions for How Many Numbers Are Smaller Than the Current Number.

终于成功了！这个方法又更快了，打败了91.45%的提交。

继续精简一下。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
        ss = sorted((e,i) for i,e in enumerate(nums))

        l = len(nums)
        smalls = [0]
        ns = [0]*l
        for i in range(1, l):
          (e0, j0) = ss[i-1]
          (e1, j1) = ss[i]
          if e0 == e1:
            smalls.append(smalls[i-1])
          else:
            smalls.append(i)

          ns[j1] = smalls[i]
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

继续。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
        ss = sorted((e,i) for i,e in enumerate(nums))

        l = len(nums)
        last = 0
        ns = [0]*l
        for i in range(1, l):
          (e0, j0) = ss[i-1]
          (e1, j1) = ss[i]
          if e0 == e1:
            pass
          else:
            last = i

          ns[j1] = last
        return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

这时我们跑到了40ms，击败了99.81%程序。

Runtime: 40 ms, faster than 99.81% of Python3 online submissions forHow Many Numbers Are Smaller Than the Current Number.

Memory Usage: 14.4 MB, less than 15.18% of Python3 online submissions for How Many Numbers Are Smaller Than the Current Number.

再来一种解法。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
      l = len(nums)
      n = [0] * 101
      max_num = 0
      for num in nums:
        n[num] += 1
        if num > max_num:
          max_num = num

      sm = [0] * (max_num + 1)
      sum = 0
      for i in range(max_num+1):
        sm[i] = sum
        sum += n[i]
      
      ns = [0] * l
      for i in range(l):
        ns[i] = sm[nums[i]]

      return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

来个稍微复杂的。

class Solution:
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
      l = len(nums)
      n = [0] * 101
      max_num = 0
      for num in nums:
        n[num] += 1
        if num > max_num:
          max_num = num

      short_n = []
      short_num = [] * l
      zn = [0] * 101
      j = 0
      for i in range(max_num+1):
        if n[i] > 0:
          zn[i] = j          
          short_n.append(n[i])          
          short_num.append(num)
          j+=1

      sm = [0] * j
      sum = 0
      for i in range(j):
        sm[i] = sum
        sum += short_n[i]
      
      ns = [0] * l
      for i in range(l):
        ns[i] = sm[zn[nums[i]]]
      return ns

# print(Solution().smallerNumbersThanCurrent([8,1,2,2,3]))

class Solution:    
 
    def smallerNumbersThanCurrent(self, nums: [int]) -> [int]:
      max_num =max(nums)

      n = [0] * (max_num + 1)
      for num in nums:
        n[num] += 1

      sorted_ls = []
      for i in range(max_num + 1):
        if n[i] > 0:
          sorted_ls.append(i)

      sm = [0] * (max_num + 1)
      sum = 0
      for i in range(len(sorted_ls)):
        v = sorted_ls[i]
        sm[v] = sum
        sum += n[v]
      
      ns = [] 
      for i in range(len(nums)):
        ns.append(sm[nums[i]])
      return ns
# print(Solution().smallerNumbersThanCurrent([72,48,32,16,10,59,83,38,1,4,68,7,67,16,5,35,99,15,55,11,24,3,63,81,16,95,35,87,24,84,57,49,42,80,34,33,82,81,31,31,7,75,100,75,22,44,54,77,89,71,81,66,7]))

练习

• 学生像上面这样类似刷上一些题目。

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