138. Copy List with Random Pointer

刷
July-06-2019

和133一样
先收集所有的NODE，建立一套新的，此时新的直接没有指针关系。
遍历新的，通过VAL来找到原来的NODE，看看原来NODE指向哪，就把当前指向新的那个位置。

public Node copyRandomList(Node head) {
    if (head == null) return null;
    Map<Integer, Node> nodes = new HashMap<>();
    Node temp = head;
    while (temp != null) {
        if (!nodes.containsKey(temp.val)) {
            nodes.put(temp.val, temp);
        }
        temp = temp.next;
    }
    
    Map<Integer, Node> copies = nodes.entrySet().stream().collect(
        Collectors.toMap(
            entry -> entry.getKey(), 
            entry -> new Node(entry.getKey(), null, null)
        ));

    
    copies.entrySet().stream().forEach(entry -> {
        int key = entry.getKey();
        Node newNode = entry.getValue();
        Node oldNode = nodes.get(key);
        if (oldNode.next != null) {
            newNode.next = copies.get(oldNode.next.val);
        }
        if (oldNode.random != null) {
            newNode.random = copies.get(oldNode.random.val);
        }

    });
    
    return copies.get(head.val);
    
}

Map<String, Long> result2 = list.stream().collect(
                Collectors.toMap(Hosting::getName, Hosting::getWebsites));

Map<Integer, String> result3 = list.stream().collect(
                Collectors.toMap(x -> x.getId(), x -> x.getName()));