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I need to read a text file and use binary search to compare if the user input matches the password in the file. I have read the algorithm of binary search, but I don't know how to compare with user input.

Searching large files is an expensive operation; therefore, your code must first check the first five criteria. If the entered password satisfies those, the program checks the entered password using binary search.

Answer :

To implement a binary search algorithm to compare user input with passwords in a text file, you can follow these steps:

Read the contents of the text file into an array or a data structure that allows random access. This will enable efficient searching.

Sort the array or data structure in ascending order. Binary search requires the elements to be sorted.

Prompt the user to enter a password.

Perform a binary search on the array or data structure to find the user input. Here's an example of how you can implement the binary search algorithm:

def binary_search(arr, low, high, key):

while low <= high:

mid = (low + high) // 2

if arr[mid] == key:

return mid

elif arr[mid] < key:

low = mid + 1

else:

high = mid - 1

return -1

If the binary search returns a valid index (not -1), it means the user input matches a password in the text file. You can then perform further actions or display a message accordingly.

Here's an example code snippet to illustrate the overall process:

def read_passwords_from_file(filename):

with open(filename, 'r') as file:

passwords = file.readlines()

return [password.strip() for password in passwords]

def main():

# Read passwords from the file

passwords = read_passwords_from_file('passwords.txt')

# Sort the passwords

passwords.sort()

# Prompt the user to enter a password

user_input = input("Enter a password: ")

# Perform binary search

index = binary_search(passwords, 0, len(passwords) - 1, user_input)

# Check the result

if index != -1:

print("Password is valid.")

else:

print("Password is invalid.")

if __name__ == '__main__':

main()

Make sure to replace 'passwords.txt' with the actual filename of your password file.

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