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SRM2 Mar 2016
SRM 685

MultiplicationTable2

Problem statement, definition, constraints, and public examples.

Problem Statement

Fox Ciel is creating a new binary operation.

The operation will be denoted $ and it will be defined on the finite set S = {0, 1, 2, ..., n-1}. I.e., for each ordered pair (i, j) of elements of S the operation (i $ j) will return some element of S.

For example, we can have S = {0, 1}, and we can define that (0 $ 0) = 0, (0 $ 1) = 1, (1 $ 0) = 0, and (1 $ 1) = 0.

Note that Ciel's operation is not necessarily symmetric. In other words, it is possible that for some i and j the operations (i $ j) and (j $ i) return two different values.

A nice concise description of the operation $ is its "multiplication table": a square table where in row i and column j we have the value (i $ j). You are given this "multiplication table" encoded as a int[] table with n^2 elements. For each valid i and j the operation (i $ j) returns the value table[i*n+j].

A subset T of S is called good if it has the following property: for any two elements i and j in T, (i $ j) is also in T.

Find and return the minimal size of a good subset of S. Note that the answer is always defined, as there always are some good subsets. For example, the entire set S is always good.

Definition

Class:
MultiplicationTable2
Method:
minimalGoodSet
Parameters:
int[]
Returns:
int
Method signature:
int minimalGoodSet(int[] table)
(be sure your method is public)

Constraints

  • n will be between 1 and 50, inclusive.
  • table will contain exactly n*n elements.
  • Each element in table will be between 0 and n-1, inclusive.

Examples

  1. {1,1,2,3,
     1,0,3,2,
     2,0,1,3,
     1,2,3,0}
    Returns: 2
    The smallest Good set is {0,1}, we can verify: 0 $ 0 = 1 0 $ 1 = 1 1 $ 0 = 1 1 $ 1 = 0
  2. {0,1,2,3,
     1,2,3,0,
     2,3,0,1,
     3,0,1,2}
    Returns: 1
    This time the answer is 1 since {0} is a Good set.
  3. {1,1,1,1,
     2,2,2,2,
     3,3,3,3,
     0,0,0,0}
    Returns: 4
    Now the only Good set is {0,1,2,3}.
  4. {0}
    Returns: 1
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