Strong Password Checker
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10 Prerequisite LeetCode Problems
“Strong Password Checker” requires string manipulation skills, attention to edge cases, and understanding of greedy algorithms. Here are 10 problems to build these foundational skills:
“Reverse String” (LeetCode Problem #344): This problem introduces the basics of string manipulation.
“Valid Anagram” (LeetCode Problem #242): This problem provides practice for basic string manipulation and character counting.
“Longest Substring Without Repeating Characters” (LeetCode Problem #3): This problem gives practice on string traversal and counting characters, which is useful for the “Strong Password Checker” problem.
“Minimum Moves to Equal Array Elements” (LeetCode Problem #453): This problem introduces a similar greedy approach used in the “Strong Password Checker” problem.
“Add Binary” (LeetCode Problem #67): This problem helps you practice formatting output strings and handling edge cases.
“Remove All Adjacent Duplicates In String” (LeetCode Problem #1047): This problem provides practice on handling repetitive characters in a string, a concept similar to the “Strong Password Checker” problem.
“Task Scheduler” (LeetCode Problem #621): This problem introduces the concept of arranging items (or characters, in the case of “Strong Password Checker”) to satisfy certain conditions, in a greedy manner.
“Candy” (LeetCode Problem #135): This problem involves a greedy algorithm and handling edge cases, similar to “Strong Password Checker”.
“Jump Game II” (LeetCode Problem #45): This problem helps to understand the concept of taking minimum steps to achieve a goal, similar to the minimum operations needed in “Strong Password Checker”.
“Gas Station” (LeetCode Problem #134): This problem involves finding an optimal solution in a circular structure using a greedy approach.


Problem Classification
Strong Password Checker  This problem requires checking the strength of a password based on some rules. This is a Password Strength Checking Problem.
Language Agnostic Coding Drills
Sets and Set Operations: The Python
set
data structure is a collection of unique elements. It supports various operations like union (&), intersection (), difference (), symmetric difference (^), and checking for subset (<=) or superset (>=). Here,set
is used to store different types of characters.String Operations: Basic string operations include indexing, slicing, concatenation, repetition, membership testing, formatting, etc. Here, strings are used to hold different sets of characters.
Logical Operations: These are boolean operations, like ‘and’, ‘or’, ’not’, etc. In this solution, ’not’ operation is used.
Boolean to Integer Conversion: In Python, True can be considered as 1 and False as 0 for arithmetic operations. This is used here to calculate
num_required_type_replaces
.List Operations: Basic list operations include indexing, slicing, modifying, concatenation, repetition, membership testing, etc. Here, a list of group lengths is used.
Itertools Groupby: The Python
itertools.groupby
function is used to group consecutive elements that are same in an iterable. It’s a powerful tool for organizing and analyzing data.Looping Constructs: Loops are used to repeat a block of code multiple times. Here, a
for
loop is used to apply the best delete operation.List Comprehension: This is a compact way of creating a new list by performing an operation on each item in an existing list.
Enumerate Function: This function adds a counter to an iterable and returns it. The returned object is an enumerate object.
Lambda Functions: These are small anonymous functions that are created using the
lambda
keyword.Min Function: This function is used to find the minimum item in an iterable or the minimum of two or more arguments.
Sum Function: This function returns the sum of all items in an iterable.
Given these concepts, the overall problemsolving approach can be described as follows:
Identify the types of characters that are missing in the given password.
Calculate the number of inserts and deletes required to make the password of a valid length (620 characters).
Group the same consecutive characters in the password and calculate the number of groups.
If the password length exceeds 20, delete the best character from the groups until the length becomes 20. Here, the best character is determined by the operation that minimizes the total replacements in all groups.
Calculate the number of replacements needed for each group to avoid having three consecutive same characters.
Return the total operations required, which is the sum of the number of deletes and the maximum of the number of type replacements, group replacements, and inserts.
Targeted Drills in Python
1. Sets and Set Operations
Drill: Create two sets and perform union, intersection, difference, and symmetric difference operations on them.


2. String Operations
Drill: Perform indexing, slicing, concatenation, repetition, and membership testing operations on a string.


3. Logical Operations
Drill: Practice logical operations with boolean values.


4. Boolean to Integer Conversion
Drill: Convert boolean values to integer and perform arithmetic operations.


5. List Operations
Drill: Perform indexing, slicing, modifying, concatenation, repetition, and membership testing operations on a list.


6. Itertools Groupby
Drill: Group consecutive same elements in a list using itertools.groupby
.


7. Looping Constructs
Drill: Use a for
loop to print numbers from 1 to 10.


8. List Comprehension
Drill: Use list comprehension to create a list of squares of numbers from 1 to 10.


9. Enumerate Function
Drill: Use enumerate
function to print index and value of elements in a list.


10. Lambda Functions
Drill: Use a lambda
function to square a number.


11. Min Function
Drill: Use min
function to find the smallest number in a list.


12. Sum Function
Drill: Use sum
function to find the sum of all numbers in a list.

