[Leetcode 138]复制带随机指针的数列Copy List with Random Pointer

题目

深复制一个list*

Node的结构包含next和random（随机指向节点）

区别

深复制 deep copy Node a=New Node(1) Node b=new Node(1) 复制值

浅复制 shallow copy  Node a=new Node(1); Node b=a; 复制地址

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null.

Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes, where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list.

For example, if there are two nodes X and Y in the original list, where X.random --> Y, then for the corresponding two nodes x and y in the copied list, x.random --> y.

Return the head of the copied linked list.

The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

• val: an integer representing Node.val
• random_index: the index of the node (range from 0 to n-1) that the random pointer points to, or null if it does not point to any node.

Your code will only be given the head of the original linked list.

 

Example 1:

Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]

Example 3:

Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]

Example 4:

Input: head = []
Output: []
Explanation: The given linked list is empty (null pointer), so return null.

 

思路

先copy存值，不考虑指针

并存储每个节点的情况

再遍历一遍，将next和random分别赋值（data.get找到节点）

 

代码

*注意用Node cur=head来俩次遍历，不要直接用head

    public Node copyRandomList(Node head) {
        if (head==null)
            return null;
        Map<Node,Node> data=new HashMap<>();
        Node cur=head;
        while(cur!=null){
            data.put(cur,new Node(cur.val));
            cur=cur.next;
        }

        cur=head;
        while (cur!=null){
            data.get(cur).next=data.get(cur.next);
            data.get(cur).random=data.get(cur.random);
            cur=cur.next;
        }


        return data.get(head);
    }