Tree from nesting levels: Difference between revisions

=={{header|Java}}==

<syntaxhighlight lang="java">

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.Stack;

public final class TreeNestingLevels {

public static void main(String[] args) {

List<List<Integer>> lists = List.of(

Arrays.asList(),

Arrays.asList( 1, 2, 4 ),

Arrays.asList( 3, 1, 3, 1 ),

Arrays.asList( 1, 2, 3, 1 ),

Arrays.asList( 3, 2, 1, 3 ),

Arrays.asList( 3, 3, 3, 1, 1, 3, 3, 3 )

);

for ( List<Integer> list : lists ) {

List<Object> tree = createTree(list);

System.out.println(list + " --> " + tree);

}

}

private static List<Object> createTree(List<Integer> list) {

List<Object> tree = new ArrayList<Object>();

Stack<List<Object>> stack = new Stack<List<Object>>();

stack.push(tree);

for ( int item : list ) {

while ( item != stack.size() ) {

if ( item > stack.size() ) {

List<Object> innerTree = new ArrayList<Object>();

stack.peek().add(innerTree);

stack.push(innerTree);

} else {

stack.pop();

}

}

stack.peek().add(item);

}

return tree;

}

}

</syntaxhighlight>

{{ out }}

<pre>

[] --> []

[1, 2, 4] --> [1, [2, [[4]]]]

[3, 1, 3, 1] --> [[[3]], 1, [[3]], 1]

[1, 2, 3, 1] --> [1, [2, [3]], 1]

[3, 2, 1, 3] --> [[[3], 2], 1, [[3]]]

[3, 3, 3, 1, 1, 3, 3, 3] --> [[[3, 3, 3]], 1, 1, [[3, 3, 3]]]

</pre>