CF 105809O - Obfuscation technique

CF 105809O - Obfuscation technique

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Solve time: 38s
Verified: yes

Solution

Problem Understanding

This is an output-only problem. There is no input at all.

The statement gives a sequence of hexadecimal byte values. Interpreting each pair of hexadecimal digits as an ASCII character reveals a hidden message. The task is simply to determine what that message is asking for and print the requested output.

Since there is no input and no computation depending on test cases, complexity is irrelevant. The entire challenge is recognizing that the provided text is hexadecimal ASCII encoding and decoding it correctly.

A common mistake is to print the decoded sentence itself instead of the value requested by the sentence.

For example, decoding

45 4C

gives

EL

but the full message decodes to:

EL CODIGO DE DESACTIVACION ES: "CODE:RUSH:TEC"

The sentence says that the deactivation code is CODE:RUSH:TEC, so that is the required output.

Approaches

The brute-force approach is to manually decode every hexadecimal byte into its ASCII character and reconstruct the sentence. Since the message is fixed, this immediately gives the answer. The amount of work is constant.

There is no need for any algorithmic optimization because the input never changes. Once the hexadecimal string is decoded, the hidden message explicitly reveals the required output.

Approach	Time Complexity	Space Complexity	Verdict
Manual hexadecimal decoding	O(1)	O(1)	Accepted
Directly print the discovered answer	O(1)	O(1)	Accepted

Algorithm Walkthrough

1. Observe that the provided text consists of hexadecimal byte values.
2. Convert each hexadecimal value to its ASCII character.
3. Reconstruct the message.
4. Read the decoded sentence:

EL CODIGO DE DESACTIVACION ES: "CODE:RUSH:TEC". 5. Print the deactivation code requested by the message:

CODE:RUSH:TEC.

Why it works

The hexadecimal sequence is a fixed encoding of an ASCII sentence. Decoding it uniquely determines the hidden message, and the message explicitly identifies the required output. Since there is no input, printing that discovered value is always correct.

Python Solution

import sys
input = sys.stdin.readline

print("CODE:RUSH:TEC")

The solution does not read any input because the problem specifies that none exists.

The hexadecimal text in the statement is constant. After decoding it once, we know the required output is always the same string. Printing that string directly is the simplest and most reliable solution.

Worked Examples

Since the problem has no input, every execution behaves identically.

Execution Trace

Step	Action	Result
1	Decode hexadecimal text	EL CODIGO DE DESACTIVACION ES: "CODE:RUSH:TEC"
2	Extract requested code	CODE:RUSH:TEC
3	Print answer	CODE:RUSH:TEC

This trace shows that the decoded sentence directly contains the value that must be printed.

Another Execution

Step	Action	Result
1	Run program	No input required
2	Execute print statement	CODE:RUSH:TEC

Because there is no input, every run produces the same correct output.

Complexity Analysis

Measure	Complexity	Explanation
Time	O(1)	Only a single fixed string is printed
Space	O(1)	No data structures are used

The program performs a constant amount of work and uses constant memory, which easily satisfies any reasonable limits.

Test Cases

# helper: run solution on input string, return output string
import sys, io

def solve():
    print("CODE:RUSH:TEC")

def run(inp: str) -> str:
    backup_stdin = sys.stdin
    backup_stdout = sys.stdout

    sys.stdin = io.StringIO(inp)
    out = io.StringIO()
    sys.stdout = out

    solve()

    sys.stdin = backup_stdin
    sys.stdout = backup_stdout

    return out.getvalue()

assert run("") == "CODE:RUSH:TEC\n", "empty input"
assert run("\n") == "CODE:RUSH:TEC\n", "extra newline"
assert run("anything\n") == "CODE:RUSH:TEC\n", "ignored data"
assert run("123 456\n789\n") == "CODE:RUSH:TEC\n", "still constant output"

Test input	Expected output	What it validates
empty input	CODE:RUSH:TEC	Official behavior
single newline	CODE:RUSH:TEC	No input processing required
arbitrary text	CODE:RUSH:TEC	Output is constant
multiple lines	CODE:RUSH:TEC	Output-only nature of the problem

Edge Cases

The main non-obvious pitfall is printing the entire decoded sentence instead of the requested code.

If the decoded text is:

EL CODIGO DE DESACTIVACION ES: "CODE:RUSH:TEC"

the correct output is:

CODE:RUSH:TEC

The algorithm handles this because it interprets the sentence and prints only the code identified by the message.

Another possible mistake is including the quotation marks.

Correct output:

CODE:RUSH:TEC

Incorrect output:

"CODE:RUSH:TEC"

The required answer is the code itself, without surrounding quotes. The provided solution prints exactly that string.