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  1. import java.util.ArrayList;
  2. import java.util.Collections;
  3. import java.util.Comparator;
  4. import java.util.List;
  5. import java.util.Objects;
  6. import java.util.stream.Collectors;
  7.  
  8. class Scratch {
  9.  
  10.     public static void main(String[] args) {
  11.         Node<Integer> root = new Node<>(8, List.of(
  12.                 new Node<>(4, List.of(
  13.                         new Node<>(1),
  14.                         new Node<>(4),
  15.                         new Node<>(3))),
  16.                 new Node<>(3, List.of(
  17.                         new Node<>(3),
  18.                         new Node<>(5),
  19.                         new Node<>(6),
  20.                         new Node<>(4))),
  21.                 new Node<>(7, List.of(
  22.                         new Node<>(12),
  23.                         new Node<>(32),
  24.                         new Node<>(3),
  25.                         new Node<>(1)))));
  26.         System.out.println(getMaxValuePerLevel(root));
  27.     }
  28.  
  29.     public static <T extends Comparable<T>> List<T> getMaxValuePerLevel(Node<T> node) {
  30.         final ArrayList<T> maxPerLevel = new ArrayList<>();
  31.         maxPerLevel.add(node.getValue());
  32.         List<Node<T>> children = node.getChildren();
  33.         while (!children.isEmpty()) {
  34.             final Node<T> defaultNode = children.get(0);
  35.             maxPerLevel.add(children.stream()
  36.                     .map(Node::getValue)
  37.                     .max(Comparator.naturalOrder())
  38.                     .orElseGet(defaultNode::getValue));
  39.             children = children.stream()
  40.                     .map(Node::getChildren)
  41.                     .flatMap(List::stream)
  42.                     .collect(Collectors.toList());
  43.         }
  44.         return maxPerLevel;
  45.     }
  46. }
  47.  
  48. class Node<T extends Comparable<T>> {
  49.     private final T value;
  50.     private final List<Node<T>> children;
  51.  
  52.     public Node(T value) {
  53.         this(value, Collections.emptyList());
  54.     }
  55.  
  56.     public Node(T value, List<Node<T>> children) {
  57.         this.value = Objects.requireNonNull(value);
  58.         this.children = Objects.requireNonNull(children).stream()
  59.                 .filter(Objects::nonNull)
  60.                 .collect(Collectors.toUnmodifiableList());
  61.     }
  62.  
  63.     public T getValue() {
  64.         return value;
  65.     }
  66.  
  67.     public List<Node<T>> getChildren() {
  68.         return children;
  69.     }
  70. }
Success #stdin #stdout 0.08s 34312KB
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[8, 7, 32]
https://ideone.com/VlEAb0
language:
Java (HotSpot 12)
created:
5 years ago
visibility:
public

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