Codingame Solution: Conway Sequence

Original problem

The Goal

Your mission is to print a specific line of the Conway sequence.


Warning! This sequence can make you ill. The reasoning is simple but unusual: Read a line aloud whilst looking at the line above and you will notice that each line (except the first) makes ​​an inventory of the previous line.

1 1
2 1
1 2 1 1
1 1 1 2 2 1
3 1 2 2 1 1

- Line 3 shows 2 1 because the line 2 contains two 1, one after the other.
- Line 4 displays 1 2 1 1 because the line 3 contains one 2 followed by one 1.
- Line 5 displays 1 1 1 2 2 1because the line 4 contains one 1followed by one 2 followed by two 1.

This sequence refers to a technique used to encode ranges in order to compress identical values ​​without losing any information. This type of method is used, amongst others, to compress images.

Your mission is to write a program that will display the line L of this series on the basis of an original number R (R equals 1 in our example).

Game Input


Line 1: The original number R of the sequence.

Line 2: The line L to display. The index of the first line is 1.

The line L of the sequence. Each element of the sequence is separated by a space.
0 < R < 100
0 < L ≤ 25

Bash Solution

We get two numbers \(R\) and \(L\), the number to start with and the number of iterations to perform. The solution is then a recursive concatination of the relevant numbers:

read R
read L

for ((i=1; i<$L; i++)); do

    for c in $R; do
        if [[ "$p" == "" ]]; then
        elif [[ "$p" == "$c" ]]; then
            t="$t$j $p "
    R="$t$j $c"

echo $R

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