Kolakoski sequence: Difference between revisions

=={{header|Java}}==

{{trans|Kotlin}}

<lang java>import java.util.Arrays;

public class Kolakoski {

private static class Crutch {

final int len;

int[] s;

int i;

Crutch(int len) {

this.len = len;

s = new int[len];

i = 0;

}

void repeat(int count) {

for (int j = 0; j < count; j++) {

if (++i == len) return;

s[i] = s[i - 1];

}

}

}

private static int nextInCycle(final int[] self, int index) {

return self[index % self.length];

}

private static int[] kolakoski(final int[] self, int len) {

Crutch c = new Crutch(len);

int k = 0;

while (c.i < len) {

c.s[c.i] = nextInCycle(self, k);

if (c.s[k] > 1) {

c.repeat(c.s[k] - 1);

}

if (++c.i == len) return c.s;

k++;

}

return c.s;

}

private static boolean possibleKolakoski(final int[] self) {

int[] rle = new int[self.length];

int prev = self[0];

int count = 1;

int pos = 0;

for (int i = 1; i < self.length; i++) {

if (self[i] == prev) {

count++;

} else {

rle[pos++] = count;

count = 1;

prev = self[i];

}

}

// no point adding final 'count' to rle as we're not going to compare it anyway

for (int i = 0; i < pos; i++) {

if (rle[i] != self[i]) {

return false;

}

}

return true;

}

public static void main(String[] args) {

int[][] ias = new int[][]{

new int[]{1, 2},

new int[]{2, 1},

new int[]{1, 3, 1, 2},

new int[]{1, 3, 2, 1}

};

int[] lens = new int[]{20, 20, 30, 30};

for (int i=0; i<ias.length; i++) {

int len = lens[i];

int[] kol = kolakoski(ias[i], len);

System.out.printf("First %d members of the sequence generated by %s: \n", len, Arrays.toString(ias[i]));

System.out.printf("%s\n", Arrays.toString(kol));

System.out.printf("Possible Kolakoski sequence? %s\n\n", possibleKolakoski(kol));

}

}

}</lang>

{{out}}

<pre>First 20 members of the sequence generated by [1, 2]:

[1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1]

Possible Kolakoski sequence? true

First 20 members of the sequence generated by [2, 1]:

[2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2]

Possible Kolakoski sequence? true

First 30 members of the sequence generated by [1, 3, 1, 2]:

[1, 3, 3, 3, 1, 1, 1, 2, 2, 2, 1, 3, 1, 2, 2, 1, 1, 3, 3, 1, 2, 2, 2, 1, 3, 3, 1, 1, 2, 1]

Possible Kolakoski sequence? true

First 30 members of the sequence generated by [1, 3, 2, 1]:

[1, 3, 3, 3, 2, 2, 2, 1, 1, 1, 1, 1, 3, 3, 2, 2, 1, 1, 3, 2, 1, 1, 1, 1, 3, 3, 3, 2, 2, 1]

Possible Kolakoski sequence? false</pre>