138. Copy List with Random Pointer

Problem¶

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|7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0|7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

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

Example 3:

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

Constraints:

• 0 <= n <= 1000
• -10**4 <= Node.val <= 10**4
• Node.random is null or is pointing to some node in the linked list.

Solve¶

De-linked list¶

c

It quite nonsense on the node->random part of the problem. This making it impossible to create new node memory by any order, and we have to re-access and adding node->random value later.

Also, we creating O(n) memory anyway, so it just better that we utilized our O(n) space to the fullest.

• This might mean create a continues array-like memory on the heap in one malloc and accessing it will be directly like an array.
• But we not have length of the Linked list provided, so we have no ideal on how to create our memory.

I go for a easier approach first, which just delinked list with a array to storing all of the pointer. This help me:

• Having a length of the List
• Keeping a record of all pointer address
• Which make finding all node->random pointed to which node easier

This information is needed for me reconstruct all node.

struct Node* copyRandomList(struct Node* head) {
    struct Node* n[1000];
    int point[1000] = {0};
    struct Node* p = head;
    int i = 0;
    int j = 0;
    int length = 0;

    n[0] = 0;

    while (p != 0) {
        n[i] = p;
        p = p->next;
        i = i + 1;
    }

    length = i;
    for (i = 0; i < length ; i ++) {
        point[i] = 0;
        // printf("%d ", point[i]);
        p = n[i]->random;
        for (j = 0; j < length; j ++) {
            if (p == n[j]) {
                point[i] = j+1;
            }
        }
        // printf("%d \n", point[i]);
    }

    for (i = length-1; i >= 0 ; i --) {
        // printf("Why?");
        p = malloc(sizeof(struct Node));
        p->val = n[i]->val;
        p->next = 0;
        if (i < length-1) {
            p->next = n[i+1];
        }
        n[i] = p;
        // printf("At %d : %d %08p\n", i, n[i]->val, n[i]);
    }

    // printf("log!\n");
    for (i = 0; i < length ; i ++) {
        // printf("%d ", point[i]);
        if (point[i] == 0) {
            n[i]->random = 0;
        } else {
            n[i]->random = n[point[i] - 1];
        }
    }
    return n[0];
}