Python Notebook

1char.isdigit() # bool

1a = set([1, 2, 3])
2b = set([2, 3, 4])
3
4a - b     # ➜ {1}
5a | b     # ➜ {1, 2, 3, 4}
6a & b     # ➜ {2, 3}
7a ^ b     # ➜ {1, 4}

1sorted(nums)    # sort-ED → has "ED" → returns nEw Data (new list)
2nums.sort()     # no "ED" → modifies in-place, returns None

1sorted(x)  # Sounds like a FUNCTION → creates NEW thing (like print(), len())
2x.sort()   # Sounds like a METHOD → modifies EXISTING thing (like .append(), .pop())

1# Example
2nums = [3, 1, 4, 1, 5]
3
4new_list = sorted(nums)    # nums unchanged, new_list = [1, 1, 3, 4, 5]
5nums.sort()                # nums is now [1, 1, 3, 4, 5], returns None
6
7# Common mistake:
8result = nums.sort()       # ❌ result is None, not the sorted list!

1# Without unpacking (nested)
2rank = 1
3country_data = ('CountryA', 2, 3, 4)
4output = (rank, country_data)
5print(output)  # (1, ('CountryA', 2, 3, 4)) ← nested!
6
7# With unpacking (flattened)
8output = (rank, *country_data)
9print(output)  # (1, 'CountryA', 2, 3, 4) ← flat! 💥

 1# 1. Flattening tuples
 2nums = (1, 2, 3)
 3result = (0, *nums)      # (0, 1, 2, 3)
 4
 5# 2. Combining lists
 6a = [1, 2]
 7b = [3, 4]
 8combined = [*a, *b]      # [1, 2, 3, 4]
 9
10# 3. Function arguments
11def my_func(a, b, c):
12    return a + b + c
13
14args = (1, 2, 3)
15my_func(*args)           # Same as my_func(1, 2, 3)

 1# extended slicing
 2# [start:stop:step]
 3# start: inclusive
 4# stop: exclusive
 5# step: optional
 6# default: start = 0, stop = len(list), step = 1
 7my_list = [10, 20, 30, 40, 50]
 8reversed_list = my_list[::-1]
 9print(reversed_list)
10
11my_string = "hello"
12reversed_string = my_string[::-1]
13print(reversed_string)
14
15# output
16# [50, 40, 30, 20, 10]
17# olleh

1text = "   example string with spaces   \n"
2trimmed_text = text.strip()
3print(f"Original: '{text}'")
4print(f"Trimmed:  '{trimmed_text}'")
5
6# Output:
7# Original: '   example string with spaces
8# '
9# Trimmed:  'example string with spaces'

 1class Solution(object):
 2    def findJudge(self, n, trust):
 3        """
 4        :type n: int
 5        :type trust: List[List[int]]
 6        :rtype: int
 7        """
 8
 9        # trust relationships are directed edges
10
11        # loop by n
12        # find from list
13        # if index is not found in list
14        # return index
15        # else return -1
16
17        nb_trusts = [0] * (n+1)
18        nb_trusted_by = [0] * (n+1)
19
20        for a, b in trust:
21            nb_trusts[a] += 1
22            nb_trusted_by[b] += 1
23
24        print("nb_trusts", nb_trusts)
25        print("nb_trusted_by", nb_trusted_by)
26
27
28        for i in range(1, n+1):
29            if nb_trusts[i] == 0 and nb_trusted_by[i] == n-1: # not trusting anyone & trusted by everyone
30                return i
31
32        return -1

1# Using accumulate for prefix sums
2prefix_sum_from_left = list(itertools.accumulate(nums))
3prefix_sum_from_right = list(itertools.accumulate(reversed(nums)))
4prefix_sum_from_right.reverse()

 1class Solution:
 2    def countPartitions(self, nums: List[int]) -> int:
 3
 4
 5        # prefix_sum_from_left = []
 6        prefix_sum_from_left = list(itertools.accumulate(nums))
 7        prefix_sum_from_right = list(itertools.accumulate(reversed(nums)))
 8        prefix_sum_from_right.reverse()
 9
10        # print("prefix_sum_from_left", prefix_sum_from_left)
11        # print("prefix_sum_from_right", prefix_sum_from_right)
12
13        count = 0
14        for i in range(1, len(nums)):
15            print("i", i)
16            if (prefix_sum_from_left[i-1] - prefix_sum_from_right[i]) % 2 == 0:
17                count += 1
18
19        return count

1total_sum = sum(nums)  # Single O(n) operation
2for num in nums[:-1]:  # O(n) iteration
3    prefix_sum += num
4    suffix_sum = total_sum - prefix_sum  # O(1) calculation

 1class Solution:
 2    def countPartitions(self, nums: List[int]) -> int:
 3        # Calculate total sum to avoid computing it multiple times.
 4        total_sum = sum(nums)
 5        print("total_sum", total_sum)
 6
 7        prefix_sum = 0
 8        count = 0
 9
10        # We only need to check up to n-1 for partitioning.
11        # for i in range(0, len(nums)-1):
12        for i in nums[:-1]:
13            prefix_sum += nums[i]
14            current_oposite = total_sum - prefix_sum
15            # print("prefix_sum", prefix_sum)
16            # print("current_oposite", current_oposite)
17
18            # Check if the difference between left and right partition sums is even.
19            if ((prefix_sum - current_oposite) % 2) == 0:
20                count += 1
21
22        return count

 1class Solution:
 2    def getMinDistance(self, nums: List[int], target: int, start: int) -> int:
 3        if nums[start] == target:
 4            return 0
 5
 6        min_dist = float('inf')
 7
 8        for i, num in enumerate(nums):
 9            if nums[i] == target:
10                min_dist = min(min_dist, abs(i - start))
11
12        return min_dist

 1class Solution:
 2    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
 3        """
 4        Do not return anything, modify nums1 in-place instead.
 5        """
 6
 7        pointer_nums1 = m - 1
 8        pointer_nums2 = n - 1
 9        pointer_placement = m + n - 1
10
11        while pointer_nums1 >= 0 and pointer_nums2 >= 0:
12            if nums1[pointer_nums1] > nums2[pointer_nums2]:
13                nums1[pointer_placement] = nums1[pointer_nums1]
14                pointer_nums1 -= 1
15            else:
16                nums1[pointer_placement] = nums2[pointer_nums2]
17                pointer_nums2 -= 1
18
19            pointer_placement -= 1
20
21        nums1[: pointer_nums2 + 1] = nums2[: pointer_nums2 + 1]
22        qwe

1# simply just
2# Create a set
3set = set()
4
5# then you can directly use the existing array to a set like
6list = [1,2,3]
7set = set(list)
8# then you can use the set to do some operations
9print(set)

1# Create a dictionary

1print()
2print("Hello", "World")
3# "Hello World"
4print("Hello", "World", sep="")
5# "HelloWorld"

1type()

1// # this forces the output to be integer

1list = [0,1,2,3]
2len(list)
3# 4
4min(list)
5# 0
6max(list)
7# 3

1print(list[0:3]) # Exclusive 3 - incl:excl
2# [0, 1, 2]

1print(list[-1])

1list.pop()
2# 3
3print(list)
4# [0,1,2]

1list.append(4)
2print(list)
3# [0,1,2,4]

1storage = (32,64,128,256)
2print(storage)
3# (32, 64, 128, 256)

1print(storage[1])
2# 64

1# creating a dictionary
2attributes = {
3    'Brand': 'Apple',
4    'RAM (in GB)': 4,
5    'Storage (in GB)': 128,
6    'Price (in $)': 800
7    }
8print(attributes)
9# {'Brand': 'Apple', 'RAM (in GB)': 4, 'Storage (in GB)': 128, 'Price (in $)': 800}

1type(attributes)
2# dict

 1# creating a dictionary for storing data.
 2products = {
 3    'Brand': brand_list,
 4    'RAM (in GB)': ram_list,
 5    'Storage (in GB)': storage_list,
 6    'Price (in $)': price_list
 7    }
 8
 9print(products)
10# {'Brand': ['Apple', 'Samsung', 'LG', 'Motorola'], 'RAM (in GB)': [4, 12, 8, 8], 'Storage (in GB)': [128, 128, 64, 128], 'Price (in $)': [900, 899, 600, 1000]}

1# keys of a dictionary
2keys = products.keys()
3print('The keys of the dictionary are :\n',keys)
4# ['Brand', 'RAM (in GB)', 'Storage (in GB)', 'Price (in $)']

1# values of a dictionary
2values = products.values()
3print('The values of the dictionary are :\n', values)
4# [['Apple', 'Samsung', 'LG', 'Motorola'], [4, 12, 8, 8], [128, 128, 64, 128], [900, 899, 600, 1000]]

1dictionary={1: "USA", 2: "India", 3: "China"}
2dictionary.update({3:"Japan"})
3print(dictionary)
4# {1: 'USA', 2: 'India', 3: 'Japan'}

1dictionary={1:"USA", 2:"India", 3:"China"}
2dictionary.pop(2)
3print(dictionary)
4# {1: 'USA', 3: 'China'}

1price = 900
2# define the budget price
3budget = int(input('Enter your budget(in dollars): '))
4
5# if-else statement
6if price <= budget:
7  print('Congrats! You can buy the Iphone')
8else:
9  print('Sorry! The mobile price is more than your budget')

1print(range(6))
2# range(0, 6)

1print(list(range(6)))
2# [0, 1, 2, 3, 4, 5]

1print(list(range(2,6)))
2# [2, 3, 4, 5]

1print(list(range(6, 14, 2))) # Iterating by 2
2# [6, 8, 10, 12]

1discounted_price_list=[]
2
3for x in price_list:
4  discounted_price = x - (x*(5/100))
5  discounted_price_list.append(discounted_price)
6
7print(discounted_price_list)

1discounted_price_list = [x - (x*(5/100)) for x in price_list]
2print(discounted_price_list)

1within_budget = []
2
3for x in discounted_price_list:
4  if x <= budget:
5    within_budget.append('Yes')
6  else:
7    within_budget.append('No')
8
9print(within_budget)

1# asking for customer's budget
2budget = int(input('Enter your budget(in dollars): '))
3
4# creating a list of Yes/No based on budget and discounted prices
5within_budget = ['Yes' if x <= budget else 'No' for x in discounted_price_list]
6print(within_budget)

1dis_price_lambda = lambda discount : 900 - ( 900 * (discount / 100) )
2# call the function with discount = 10%
3dis_price_lambda(10)
4# 810.0

1def say(message, times):
2    print(message*times)
3say("How are you", 2)
4# How are youHow are you

1(lambda x: (x+2)*5/2)(4)
2# 15.0

 1def total_amount(price1, price2, price3, price4, price5):
 2    """
 3    This function takes the price of five phones ordered
 4    and returns the total order amount.
 5    """
 6    # computing the total order amount
 7    total = price1 + price2 + price3 + price4 + price5
 8
 9    # return the total amount
10    return total
11
12print('Total order amount:', total_amount(700, 599, 650, 900, 820))
13# Total order amount: 3669

 1def total_amount(*args): # can be renamed to *prices
 2    """
 3    This function takes the prices of phones ordered
 4    and returns the total order amount.
 5    """
 6    total = 0
 7    # computing the total order amount
 8    for arg in args:
 9        total += arg
10
11    # return the total amount
12    return total
13
14print('Total order amount:', total_amount(700, 599, 650, 900, 820))
15# Total order amount: 3669
16print('Total order amount:', total_amount(700, 599, 650, 900, 820, 630, 520, 799, 999, 840))
17# Total order amount: 7457

 1def customer_net_spend(*prices, discount=0.0, **kwargs):
 2    """
 3    This function takes the prices of phones ordered,
 4    the discount percentage, and any other cost additions/subtractions,
 5    and returns the customer's net spend on the order.
 6    """
 7    total = 0
 8    # computing the total order amount
 9    for price in prices:
10        total += price
11
12    total_discounted_price = total - discount*total
13
14    net_spend = total_discounted_price - kwargs['cashback']
15
16    # return the total amount
17    return net_spend
18
19additionals = {'cashback': 5}
20print('Customer net spend (during last day of festive season):', customer_net_spend(700, 599, 650, discount=0.05, **additionals))
21# Customer net spend (during last day of festive season): 1846.55

 1def order_summary(*prices, **additionals):
 2    """
 3    This function takes the prices of phones ordered
 4    and any other cost additions/subtractions,
 5    and returns the total amount, net spend,
 6    and rewards points earned for the order.
 7    """
 8    total = 0
 9    # computing the total order amount
10    for price in prices:
11        total += price
12
13    net_spend = total - additionals['discount']*total - additionals['cashback']
14
15    if total >= 10000:
16        reward_points = 300
17    elif total >= 5000:
18        reward_points = 200
19    elif total >= 2000:
20        reward_points = 100
21    else:
22        reward_points = 0
23
24    # return the total amount
25    return total, net_spend, reward_points # Is going to return as tuple
26
27additionals = {'discount':0.05, 'cashback': 5}
28ta, ns, rp = order_summary(700, 599, 750, **additionals)
29print('Customer Order Summary:\n', '\nTotal Amount:', ta, '\nTotal Discounted Amount:', ns, '\nReward Points Earned:', rp)
30
31# Customer Order Summary:
32#
33# Total Amount: 2049
34# Total Discounted Amount: 1941.55
35# Reward Points Earned: 100

1def my_function(a, b, **kwargs, *args):
2    return a+b
3my_function(5,6)

 1def my_function(a, b, *args, **kwargs):
 2    print("a:", a)
 3    print("b:", b)
 4    print("args:", args)
 5    print("kwargs:", kwargs)
 6
 7my_function(1, 2, 3, 4, 5, x=6, y=7)
 8# a: 1
 9# b: 2
10# args: (3, 4, 5)
11# kwargs: {'x': 6, 'y': 7}

1def fun(A, B=30):
2    return A + B
3
4# A is a positional argument and B is a keyword argument

1list_mul = ['2','2','2']
2list_mul*2