import java.util.*;
import java.util.function.*;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;

class Splitting {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("a", 1);
        map.put("b", 2);

        for(int depth: new int[] { 1, 2, Integer.MAX_VALUE }) {
            System.out.println("With max depth: "+depth);
            Tree<Spliterator<Map.Entry<String, Integer>>> spTree
                = split(map.entrySet().spliterator(), depth);
            Tree<String> valueTree = spTree.map(sp -> "estimated: "+sp.estimateSize()+" "
                +StreamSupport.stream(sp, false).collect(Collectors.toList()));
            System.out.println(valueTree);
        }
    }

    private static <T> Tree<Spliterator<T>> split(Spliterator<T> sp, int depth) {
        Spliterator<T> prefix = depth-- > 0? sp.trySplit(): null;
        return prefix == null?
            new Tree<>(sp): new Tree<>(null, split(prefix, depth), split(sp, depth));
    }

    public static class Tree<T> {
        final T value;
        List<Tree<T>> children;

        public Tree(T value) {
            this.value = value;
            children = Collections.emptyList();
        }
        public Tree(T value, Tree<T>... ch) {
            this.value = value;
            children = Arrays.asList(ch);
        }
        public <U> Tree<U> map(Function<? super T, ? extends U> f) {
            Tree<U> t = new Tree<>(value == null? null: f.apply(value));
            if(!children.isEmpty()) {
                t.children = new ArrayList<>(children.size());
                for(Tree<T> ch: children) t.children.add(ch.map(f));
            }
            return t;
        }
        public @Override String toString() {
            if(children.isEmpty()) return value == null? "": value.toString();
            final StringBuilder sb = new StringBuilder(100);
            toString(sb, 0, 0);
            return sb.toString();
        }
        public void toString(StringBuilder sb, int preS, int preEnd) {
            final int myHandle = sb.length() - 2;
            sb.append(value == null? "": value).append('\n');
            final int num = children.size() - 1;
            if (num >= 0) {
                if (num != 0) {
                    for (int ix = 0; ix < num; ix++) {
                        int nPreS = sb.length();
                        sb.append(sb, preS, preEnd);
                        sb.append("\u2502 ");
                        int nPreE = sb.length();
                        children.get(ix).toString(sb, nPreS, nPreE);
                    }
                }
                int nPreS = sb.length();
                sb.append(sb, preS, preEnd);
                final int lastItemHandle = sb.length();
                sb.append("  ");
                int nPreE = sb.length();
                children.get(num).toString(sb, nPreS, nPreE);
                sb.setCharAt(lastItemHandle, '\u2514');
            }
            if (myHandle > 0) {
                sb.setCharAt(myHandle, '\u251c');
                sb.setCharAt(myHandle + 1, '\u2500');
            }
        }
    }
}