O(n) Reverse Arrays to Make Equal with Python

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Reverse to Make EqualCompare two arrays without sorting themPython

Given two arrays A and B of length N, determine if there is a way to make A equal to B by reversing any subarrays from array B any number of times.

Signature bool areTheyEqual(int[] arr_a, int[] arr_b)

Input All integers in array are in the range [0, 1,000,000,000].

Output Return true if B can be made equal to A, return false otherwise.

Example A = [1, 2, 3, 4] B = [1, 4, 3, 2] output = true

After reversing the subarray of B from indices 1 to 3, array B will equal array A.

SOlution:

O(n) Contiguous Subarray in Python

O(n) Contiguous Subarray in Python

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You are given an array arr of N integers. For each index i, you are required to determine the number of contiguous subarrays that fulfills the following conditions:

  • The value at index i must be the maximum element in the contiguous subarrays, and
  • These contiguous subarrays must either start from or end on index i.

Signature int[] countSubarrays(int[] arr)Input

  • Array arr is a non-empty list of unique integers that range between 1 to 1,000,000,000
  • Size N is between 1 and 1,000,000

Output An array where each index i contains an integer denoting the maximum number of contiguous subarrays of arr[i]Example: arr = [3, 4, 1, 6, 2] output = [1, 3, 1, 5, 1]Explanation:

  • For index 0 – [3] is the only contiguous subarray that starts (or ends) with 3, and the maximum value in this subarray is 3.
  • For index 1 – [4], [3, 4], [4, 1]
  • For index 2 – [1]
  • For index 3 – [6], [6, 2], [1, 6], [4, 1, 6], [3, 4, 1, 6]
  • For index 4 – [2]

So, the answer for the above input is [1, 3, 1, 5, 1]

Solution in Python O(n)

O(n) Rotational Cipher in Python

O(n) Rotational Cipher in Python

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Rotational Cipher: One simple way to encrypt a string is to “rotate” every alphanumeric character by a certain amount. Rotating a character means replacing it with another character that is a certain number of steps away in normal alphabetic or numerical order. For example, if the string “Zebra-493?” is rotated 3 places, the resulting string is “Cheud-726?”. Every alphabetic character is replaced with the character 3 letters higher (wrapping around from Z to A), and every numeric character replaced with the character 3 digits higher (wrapping around from 9 to 0). Note that the non-alphanumeric characters remain unchanged. Given a string and a rotation factor, return an encrypted string.

Signature

string rotationalCipher(string input, int rotationFactor)

Input

1 <= |input| <= 1,000,000 0 <= rotationFactor <= 1,000,000

Output

Return the result of rotating input a number of times equal to rotationFactor.

Example 1

input = Zebra-493?

rotationFactor = 3

output = Cheud-726?

Example 2

input = abcdefghijklmNOPQRSTUVWXYZ0123456789

rotationFactor = 39

output = nopqrstuvwxyzABCDEFGHIJKLM9012345678

O(n) Solution in Python:

Test 1:

PS C:\dev\scripts> .\test_rotational_cipher_python.py
Length Dic Numbers : 10
Length Dic lowercase : 26
Length Dic uppercase : 26
Input: Zebra-493?
Output: Cheud-726?

Test2:

PS C:\dev\scripts> .\test_rotational_cipher_python.py
Length Dic Numbers : 10
Length Dic lowercase : 26
Length Dic uppercase : 26
Input: abcdefghijklmNOPQRSTUVWXYZ0123456789
Output: nopqrstuvwxyzABCDEFGHIJKLM9012345678

Pair Sum with Python O(n)

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Given a list of n integers arr[0..(n-1)], determine the number of different pairs of elements within it which sum to k. If an integer appears in the list multiple times, each copy is considered to be different; that is, two pairs are considered different if one pair includes at least one array index which the other doesn’t, even if they include the same values.

Signature

int numberOfWays(int[] arr, int k)

Input

n is in the range [1, 100,000]. Each value arr[i] is in the range [1, 1,000,000,000]. k is in the range [1, 1,000,000,000].

Output

Return the number of different pairs of elements which sum to k.

Example 1

n = 5 k = 6 arr = [1, 2, 3, 4, 3] output = 2The valid pairs are 2+4 and 3+3.

Example 2

n = 5 k = 6 arr = [1, 5, 3, 3, 3] output = 4There’s one valid pair 1+5, and three different valid pairs 3+3 (the 3rd and 4th elements, 3rd and 5th elements, and 4th and 5th elements).

Solution using Python:

Pair Sum with Python

Complexity:

  • Time: O(n)
  • Space: Array of n and Hash of n (Who cares about space?? really ??)

Execution:

Case 1:

[1, 2, 3, 4, 3]
{1: 1, 2: 1, 3: 2, 4: 1}
Total Pairs is: 2.0

Case 2:

[1, 5, 3, 3, 3]
{1: 1, 5: 1, 3: 3}
Total Pairs is: 4.0

AWS Lambda to auto start stop Ec2 instance on schedule using python and boto3

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Use this lambda function to auto start stop all Ec2 instances based on schedule from tags.

aws ec2 auto start stop lambda


#Auto Shutodown - Start EC2 instances based on tags
import boto3
import os
import json
import croniter
import datetime
# Enter the region your instances are in. Include only the region without specifying Availability Zone; e.g., 'us-east-1'
region = 'us-west-2'

EC2_STATUS_CODE_RUNNING = 16
EC2_STATUS_CODE_STOPPED = 80

def lambda_handler(event, context):
ec2 = boto3.client('ec2', region_name=region)

#auto_start_stop_tag = 'tc:uptime_schedule_gmt'
auto_start_tag = 'tc:start_time_schedule_gmt_24h_format'
auto_shutdown_tag = 'tc:shutdown_time_schedule_gmt_24h_format'

instances_to_shutdown = []
instances_to_start = []
# Query ec2 machines for auto_start_stop_tag,
#instances_with_schedules = get_instance_schedules(auto_start_stop_tag)
instances_with_start_schedules = get_instance_schedules(auto_start_tag)
instances_with_shutdown_schedules = get_instance_schedules(auto_shutdown_tag)
print("instances_with_start_schedules: %s" % instances_with_start_schedules)
print("instances_with_shutdown_schedules: %s" % instances_with_shutdown_schedules)

for instance_id, values in instances_with_start_schedules.items():
now = datetime.datetime.now()
print("now: %s" % now)
iterator = croniter.croniter(values['Schedule'], now)
next_run_time = iterator.get_next(datetime.datetime)
print("next_run_time: %s" % next_run_time)
duration_until_next_run_time = next_run_time - now
print("duration_until_next_start_time: %s" % duration_until_next_run_time)
duration_of_one_hour = datetime.timedelta(hours=1)

if duration_until_next_run_time <= duration_of_one_hour and values['State']['Code'] == EC2_STATUS_CODE_STOPPED: print("true") print("instance_to_stop.append(%s)" % instance_id) instances_to_start.append(instance_id) for instance_id, values in instances_with_shutdown_schedules.items(): now = datetime.datetime.now() print("now: %s" % now) iterator = croniter.croniter(values['Schedule'], now) next_run_time = iterator.get_next(datetime.datetime) print("next_run_time: %s" % next_run_time) duration_until_next_run_time = next_run_time - now print("duration_until_next_shutdown_time: %s" % duration_until_next_run_time) duration_of_one_hour = datetime.timedelta(hours=1) if duration_until_next_run_time <= duration_of_one_hour and values['State']['Code'] == EC2_STATUS_CODE_RUNNING: print("instance_to_shutdown.append(%s)" % instance_id) instances_to_shutdown.append(instance_id) if len(instances_to_shutdown) > 0:
ec2.stop_instances(InstanceIds=instances_to_shutdown)
print('stopped your instances: ' + str(instances_to_shutdown))
send_shutdown_notification(instances_to_shutdown, "STOPPED")

if len(instances_to_start) > 0:
ec2.start_instances(InstanceIds=instances_to_start)
print('started your instances: ' + str(instances_to_start))
send_start_notification(instances_to_start, "STARTED")

def send_shutdown_notification(instances, event):
instances_json_object = {"instances":instances, "event":event}
instances_json_string = json.dumps(instances_json_object)
instances_json_bytes = instances_json_string.encode('utf-8')

lambda_arn = os.environ['LAMBDA_NOTIFICATION_SHUTDOWN_ARN']
lambda_client = boto3.client("lambda")
lambda_client.invoke(
FunctionName=lambda_arn,
InvocationType='Event',
LogType='None',
Payload=instances_json_bytes
)

def send_start_notification(instances, event):
instances_json_object = {"instances":instances, "event":event}
instances_json_string = json.dumps(instances_json_object)
instances_json_bytes = instances_json_string.encode('utf-8')

lambda_arn = os.environ['LAMBDA_NOTIFICATION_START_ARN']
lambda_client = boto3.client("lambda")
lambda_client.invoke(
FunctionName=lambda_arn,
InvocationType='Event',
LogType='None',
Payload=instances_json_bytes
)

def get_instance_schedules(tag_name):
# When passed a tag key, tag value this will return a list of InstanceIds that were found.

ec2client = boto3.client('ec2')

response = ec2client.describe_instances(
Filters=[
{
'Name': 'tag-key',
'Values': [tag_name]
}
]
)
instancelist = {}
for reservation in (response["Reservations"]):
for instance in reservation["Instances"]:
tag_value = ''
for tag in instance['Tags']:
if tag['Key'] == tag_name:
tag_value = tag['Value']
break
instancelist[instance["InstanceId"]] = {'Schedule':tag_value,'State':instance['State']}

return instancelist