题目来源

1、将每个 拷贝节点 都 插入 在原来的节点的后面

2、链接每个拷贝结点的 random

注意：

3、将拷贝结点 解 下来，尾插到一起，恢复原来链表。

/**
 * Definition for a Node.
 * struct Node {
 *     int val;
 *     struct Node *next;
 *     struct Node *random;
 * };
 */

struct Node* copyRandomList(struct Node* head) {
    //1 将每个 拷贝节点 都 插入 在原来的节点的后面
    struct Node* cur = head;
    while(cur){
        struct Node* next = cur->next;
        struct Node* copy = (struct Node*)malloc(sizeof(struct Node));
        //拷贝结点的值和cur的值相同
        copy->val = cur->val;

        //将拷贝结点插入在cur的后面
        cur->next =copy;
        copy->next = next;

        //往后走
        cur = next;
    }

    //2 链接每个拷贝结点的 random
    cur =  head;
    while(cur){
        struct Node* copy = cur->next;

        //链接random
        if(cur->random == NULL)
            copy->random = NULL;
        else
            copy->random = cur->random->next;//注意

        cur = copy->next;
    }

    //3 将拷贝结点 解 下来，尾插到一起，恢复原来链表。
    cur = head;
    struct Node* copyhead = NULL;
    struct Node* copytail = NULL;
    while(cur){
        struct Node* copy = cur->next;
        struct Node* next = copy->next;

        //最开始为空
        if(copytail == NULL)
            copyhead = copytail = copy;
        else{
            copytail->next = copy;
            copytail = copytail->next;
        }

        //恢复原来的链表
        cur->next = next;
        //注意
        cur = next;
    }
    return copyhead;
}