Task: Nonoblock
C: #include <stdio.h>
#include <string.h>

void nb(int cells, int total_block_size, int* blocks, int block_count,
        char* output, int offset, int* count) {
    if (block_count == 0) {
        printf("%2d  %s\n", ++*count, output);
        return;
    }
    int block_size = blocks[0];
    int max_pos = cells - (total_block_size + block_count - 1);
    total_block_size -= block_size;
    cells -= block_size + 1;
    ++blocks;
    --block_count;
    for (int i = 0; i <= max_pos; ++i, --cells) {
        memset(output + offset, '.', max_pos + block_size);
        memset(output + offset + i, '#', block_size);
        nb(cells, total_block_size, blocks, block_count, output,
           offset + block_size + i + 1, count);
    }
}

void nonoblock(int cells, int* blocks, int block_count) {
    printf("%d cells and blocks [", cells);
    for (int i = 0; i < block_count; ++i)
        printf(i == 0 ? "%d" : ", %d", blocks[i]);
    printf("]:\n");
    int total_block_size = 0;
    for (int i = 0; i < block_count; ++i)
        total_block_size += blocks[i];
    if (cells < total_block_size + block_count - 1) {
        printf("no solution\n");
        return;
    }
    char output[cells + 1];
    memset(output, '.', cells);
    output[cells] = '\0';
    int count = 0;
    nb(cells, total_block_size, blocks, block_count, output, 0, &count);
}

int main() {
    int blocks1[] = {2, 1};
    nonoblock(5, blocks1, 2);
    printf("\n");
    
    nonoblock(5, NULL, 0);
    printf("\n");

    int blocks2[] = {8};
    nonoblock(10, blocks2, 1);
    printf("\n");
    
    int blocks3[] = {2, 3, 2, 3};
    nonoblock(15, blocks3, 4);
    printf("\n");
    
    int blocks4[] = {2, 3};
    nonoblock(5, blocks4, 2);

    return 0;
}

Java: import java.util.*;
import static java.util.Arrays.stream;
import static java.util.stream.Collectors.toList;

public class Nonoblock {

    public static void main(String[] args) {
        printBlock("21", 5);
        printBlock("", 5);
        printBlock("8", 10);
        printBlock("2323", 15);
        printBlock("23", 5);
    }

    static void printBlock(String data, int len) {
        int sumChars = data.chars().map(c -> Character.digit(c, 10)).sum();
        String[] a = data.split("");

        System.out.printf("%nblocks %s, cells %s%n", Arrays.toString(a), len);
        if (len - sumChars <= 0) {
            System.out.println("No solution");
            return;
        }

        List<String> prep = stream(a).filter(x -> !"".equals(x))
                .map(x -> repeat(Character.digit(x.charAt(0), 10), "1"))
                .collect(toList());

        for (String r : genSequence(prep, len - sumChars + 1))
            System.out.println(r.substring(1));
    }

    
    static List<String> genSequence(List<String> ones, int numZeros) {
        if (ones.isEmpty())
            return Arrays.asList(repeat(numZeros, "0"));

        List<String> result = new ArrayList<>();
        for (int x = 1; x < numZeros - ones.size() + 2; x++) {
            List<String> skipOne = ones.stream().skip(1).collect(toList());
            for (String tail : genSequence(skipOne, numZeros - x))
                result.add(repeat(x, "0") + ones.get(0) + tail);
        }
        return result;
    }

    static String repeat(int n, String s) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++)
            sb.append(s);
        return sb.toString();
    }
}