CODEVITA (TCS)
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CodeVita Round 1 2020 question Season 9
CodeVita :
Number Distancing
- Problem Description
Consider 9 natural numbers arranged
in a 3x3 matrix:
n11 n12 n13
n21 n22 n23
n31 n32 n33
Define numbers "in
contact" with a given number to be those that appear closest to it on the
same row, column or diagonally across:
Contacts of number n11: n12, n22 and
n21
Contacts of number n12: n11, n21,
n22, n23, n13
Contacts of number n13: n12, n22,
n23
Contacts of number n21: n11, n12,
n22, n32, n31
Contacts of number n22: n11, n12,
n13, n23, n33, n32, n31, n21
Contacts of number n23: n13, n12,
n22, n32, n33
Contacts of number n31: n21, n22,
n32
Contacts of number n32: n31, n21,
n22, n23, n33
Contacts of number n33: n32, n22,
n23
The problem now is that numbers
having a common factor (other than 1) should not be "in contact". In
other words, a pair of numbers can remain neighbours only if their highest
common factor is 1.
The following rules apply to enforce
this "distancing":
1. The central number (n22) stays
put.
2. The corner numbers (n11, n13,
n33, n31) can move in the same row or column or diagonally away from the
centre.
3. The numbers "on the
walls" (n12, n23, n32, n21) can only move from the walls i.e. n21 can only
move "left", n12 can only move "up", n23 can only move
"right" and n32 can only move "down".
4. Each number should stay put as
far as possible and the "distancing" operation should result in the
least number of numbers ending up without any contacts.
5. After satisfying rule 4, if there
are multiple options for the final matrix, then the "distancing"
operation should result in the smallest (m x n matrix, including the
intervening blank space elements, with the least possible value of m*n).
6. If, after satisfying all the
rules above, there are multiple distancing options for a set of numbers, the
largest number keeps to its original cell.
First line consists of 9 space
separated integers denoting n11, n12, n13, .... n23, n33 respectively.
23 33 12 1 2 5 25 6 10
- Explanation
Initial configuration
23 33 12
1 2 5
25 6 10
The optimal distancing options
result in the following possibility (space denoted by *):
23 33 * 12
1 2 5 *
25 * * *
* 6 * 10
10 ends up as the number without
contacts.
1 2 3 4 5 6 7 8 9
- Explanation
Initial configuration:
1 2 3
4 5 6
7 8 9
The optimal distancing options
result in the following 5x3 matrix (space denoted by *):
* 2 3
1 * *
4 5 6
7 * *
* 8 9
There is finally no number without a
contact.
2 6 2 10 19 12 2 20 2
- Explanation
Initial Configuration:
Approach 1) Moving 6 and 20
Final Matrix
2 * 6 * 2
* * * * *
* 10 19 12 *
* * * * *
2 * 20 * 2
Approach 2) Moving 10 and 12
2 * * * 2
* * 6 * *
10 * 19 * 12
* * 20 * *
2 * * * 2
We prefer approach 2) and not 1) since the largest of all the elements (20) needs to be retained in it's original cell.
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