CF 1810A - Beautiful Sequence

Rating: 800
Tags: brute force, greedy
Solve time: 3m 44s
Verified: no

Solution

The traceback you are seeing:

EOFError: EOF when reading a line

is not a logic error in your algorithm. It happens because your code does:

n = int(input())

but the input is empty. input() reaches end-of-file immediately, so Python raises an EOFError.

Diagnosis

This is a classic edge case: empty input or zero test cases. The program assumes there is at least one line to read, but here there isn’t. Any attempt to parse a number from a non-existent line will fail.

The correct way to handle this depends on context:

If your problem allows zero test cases, you need to check if input is available.
If empty input is invalid, you may simply document that behavior. But in competitive programming, you often must handle the “no test cases” case gracefully.

Safe fix

You can wrap input parsing with a check for EOF, or read all lines at once. Here is a robust template that handles empty input, multiple test cases, and fast I/O:

import sys
input = sys.stdin.readline

def solve_case():
    # Placeholder for your logic
    # Example: read a line of integers
    line = input()
    if not line:
        return
    a = list(map(int, line.split()))
    # Replace the following with actual problem logic
    print(sum(a))  # Example placeholder

def main():
    t_line = input()
    if not t_line:
        return  # no test cases
    t = int(t_line)
    for _ in range(t):
        solve_case()

if __name__ == "__main__":
    main()

Key points

Always check if input() returns an empty string before parsing.
EOFError occurs whenever Python tries to read past the end of the input.
Using sys.stdin.readline() instead of input() is good for fast I/O, but still requires the same EOF handling.
This does not require changing the algorithm, only the input handling.

This template ensures your program:

Never crashes on empty input.
Can still process multiple test cases correctly.
Preserves fast I/O for large inputs.