CCO '18 P2 - Wrong Answer

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Points: 12 (partial)
Time limit: 1.0s
Memory limit: 512M

Problem type

Canadian Computing Olympiad: 2018 Day 1, Problem 2

Troy made the following problem (titled WA) for a programming contest:

There is a game with N levels numbered from 1 to N. There are two characters, both are initially at level 1. For i<j, it costs A_{i,j} coins to move a character from level i to level j. It is not allowed to move a character from level i to level j if i>j. To win the game, every level (except level 1) must be visited by exactly one character. What is the minimum number of coins needed to win?

JP is a contestant and submitted the following Python solution.

def Solve(N, A):
    # A[i][j] is cost of moving from level i to level j
    # N is the number of levels
    x, y, sx, sy = 1, 1, 0, 0 # Initialize x and y to 1, sx and sy to 0
    for i in range(2, N + 1): # loop from 2 to N
        if sx + A[x][i] < sy + A[y][i]:
            sx += A[x][i]
            x = i
            sy += A[y][i]
            y = i
    return sx + sy

Troy is certain that JP's solution is wrong. Suppose for an input to WA, JP's solution returns X but the minimum number of coins needed is Y. To show how wrong JP's solution is, help Troy find an input N and A_{i,j} such that \dfrac{x}{y} is maximized.

Input Specification

There is no input.

Output Specification

Print an input to WA in the following format:

On the first line, print one integer N\,(2\leq N\leq100).

Then print N-1 lines; the i-th line should contain N-i integers A_{i,i+1},\ldots,A_{i,N}\,(1\leq A_{i,j}\leq100).

If your output is not in the correct format, it will get an incorrect verdict on the sample test in the grader and score 0 points.

Otherwise, suppose that for your input, JP's solution returns X but the minimum number of coins needed is Y. Then you will receive \left\lceil \min\left(25,\dfrac{X}{4Y}\right)\right\rceil points where \lceil Z \rceil is the smallest integer that is not less than Z.

Sample Output

1 2 3 4
10 9 8
7 6

Explanation for Sample Output

The optimal way to win the game is for one character to visit level 2 and the other character to visit levels 3, 4 and 5. This costs (1)+(2+7+5)=15 coins. JP's solution returns 18. Thus \dfrac{X}{4Y}=\dfrac{18}{4\times15}=0.3, so this output will receive \lceil0.3\rceil=1 point.


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