leetcode 138. Copy List with Random Pointer ----- java

Posted 2020-08-19 xiaoba1203

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

Return a deep copy of the list.

 

和第133题差不多，都是图的复制，区别在于这道题的label有可能是相同的，所以导致了map的key有可能相同，所以需要处理。

两种方法差不多。第二种更简洁。

 

1、在复制next之后修改原结构的label为顺序增长，方便建立map，之后再修改回来。

/**
 * Definition for singly-linked list with a random pointer.
 * class RandomListNode {
 *     int label;
 *     RandomListNode next, random;
 *     RandomListNode(int x) { this.label = x; }
 * };
 */
public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if( head == null )
            return null;
        Map map2 = new HashMap<Integer,RandomListNode>();
        int num = 1;


        RandomListNode node = head;
        RandomListNode newNode = new RandomListNode(head.label);
        RandomListNode node2 = newNode;
        map2.put(0,node2);
        node.label = 0;

        node = node.next;
        while( node != null ){
            RandomListNode nextNode = new RandomListNode(node.label);
            node2.next = nextNode;
            node2 = node2.next;
            node.label = num;
            map2.put(num,node2);
            num++;
            node = node.next;

        }

        node = head;
        node2 = newNode;


        while( node != null ){

            if( node.random == null){
                node = node.next;
                node2 = node2.next;
                continue;
            }

            node2.random = (RandomListNode) map2.get( node.random.label );

            node = node.next;
            node2 = node2.next;

        }
        node2 = newNode;
        node = head;
        while( node != null ){
            node.label = node2.label;
            node = node.next;
            node2 = node2.next;
        }


        return newNode;

        
    }
}

2、建立map的时候使用

 Map<RandomListNode,RandomListNode>

 

/**
 * Definition for singly-linked list with a random pointer.
 * class RandomListNode {
 *     int label;
 *     RandomListNode next, random;
 *     RandomListNode(int x) { this.label = x; }
 * };
 */
public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        
        if( head == null )
            return null;
        Map<RandomListNode,RandomListNode> map = new HashMap<RandomListNode,RandomListNode>();


        RandomListNode node = head;
        while( node != null ){
            map.put(node,new RandomListNode(node.label));
            node = node.next;
        }
        node = head;
        while( node != null ){
            
            map.get(node).next = map.get(node.next);
            map.get(node).random = map.get(node.random);
            node = node.next;

        }
        return map.get(head);
        
    }
}