CF 1396B - Stoned Game

The traceback tells us exactly what happened: The code is trying to read an edge of a tree as two integers u v. But the actual input is: Let's trace it: First test case: Then the next line is which is an array of length 7.

codeforcescompetitive-programmingbrute-forceconstructive-algorithmsgamesgreedy

CF 1396B - Stoned Game

Rating: 1800
Tags: brute force, constructive algorithms, games, greedy
Solve time: 11m 46s
Verified: yes

Solution

The traceback tells us exactly what happened:

u, v = map(int, input().split())
ValueError: too many values to unpack (expected 2)

The code is trying to read an edge of a tree as two integers u v.

But the actual input is:

3
7
4 6 11 11 15 18 20
4
10 10 10 11
3
1 1 1000000000

Let's trace it:

t = 3

First test case:

n = 7

Then the next line is

4 6 11 11 15 18 20

which is an array of length 7.

The submitted code incorrectly assumes that after reading n, it should read n-1 tree edges. It executes:

u, v = map(int, input().split())

on

4 6 11 11 15 18 20

which contains 7 integers, not 2.

Python cannot unpack 7 values into two variables, so it throws:

ValueError: too many values to unpack

So this is not a small bug in the implementation. The program is solving an entirely different problem, one involving trees, while the input clearly describes arrays.

The expected output

2 3 6
-1
1 2 3

also is not a YES/NO answer and not a tree-cleaning answer. It corresponds to a different Codeforces problem altogether.

Because the actual problem statement/code that produced this output is missing, there is not enough information to reconstruct the correct algorithm. We only have:

Input:
3
7
4 6 11 11 15 18 20
4
10 10 10 11
3
1 1 1000000000

Output:
2 3 6
-1
1 2 3

Many completely different problems could produce that output.

To provide a corrected solution, I need the actual problem statement (or at least the Codeforces problem number/title). Right now the only thing that can be diagnosed with certainty is:

  1. The submitted code expects a tree.
  2. The input contains arrays.
  3. The parser fails immediately on the first array line.
  4. The algorithm is for the wrong problem, so a targeted fix is impossible without knowing the intended problem.

Please provide the problem statement or Codeforces problem ID, and I can derive and implement the correct solution.