September 22, 2019

138. Copy List with Random Pointer

使用 hashmap，第一遍建立原节点和新节点的hashmap，第二遍给next和random指针赋值。
Time = O(n), space = O(n)

/*
// Definition for a Node.
class Node {
    public int val;
    public Node next;
    public Node random;

    public Node() {}

    public Node(int _val,Node _next,Node _random) {
        val = _val;
        next = _next;
        random = _random;
    }
};
*/
class Solution {
    public Node copyRandomList(Node head) {
        if (head == null) {
            return null;
        }
        Node cur = head;
        Map<Node, Node> map = new HashMap<>();
        while (cur != null) {
            map.put(cur, new Node(cur.val, null, null));
            cur = cur.next;
        }
        cur = head;
        while (cur != null) {
            map.get(cur).next = map.get(cur.next);
            map.get(cur).random = map.get(cur.random);
            cur = cur.next;
        }
        return map.get(head);
    }
}