映射法数据深度复制

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本文详细介绍了如何通过映射关系（unordered_map）在复杂数据结构中进行深度复制，以解决带有随机指针节点的链表复制问题及无向图节点复制问题。采用BFS和DFS两种遍历方式实现复制过程，强调了映射关系在复制复杂数据结构时的重要性。

问题一：

Copy List with Random Pointe

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.

/**
* Definition for singly-linked list with a random pointer.
* struct RandomListNode {
*     int label;
*     RandomListNode *next, *random;
*     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
* };
*/

方法一：BFS

    RandomListNode *copyRandomList(RandomListNode *head)
    {
        if (!head) return NULL;
        unordered_map<RandomListNode*, RandomListNode*> mapping;
        mapping[head] = new RandomListNode(head->label);
        queue<RandomListNode*> que;
        que.push(head);
        while (!que.empty())
        {
            RandomListNode* temp = que.front();
            que.pop();
            if (temp->next)
            {
                if(mapping.find(temp->next) == mapping.end())
                {
                    mapping[temp->next] = new RandomListNode(temp->next->label);
                    que.push(temp->next);
                }
                mapping[temp]->next = mapping[temp->next];
            }
            if (temp->random)
            {
                if(mapping.find(temp->random) == mapping.end())
                {
                    mapping[temp->random] = new RandomListNode(temp->random->label);
                    que.push(temp->random);
                }
                mapping[temp]->random = mapping[temp->random];
            }
        }
        return mapping[head];
    }

方法二：DFS

    unordered_map<RandomListNode*, RandomListNode*> mapping;
    RandomListNode *copyRandomList(RandomListNode *head) {
        // 如果为NULL直接返回NULL
        if (!head) return NULL;
        // 判断节点参数是否已经在映射对中，如果没有则新建节点，并对其指针进行赋值
        // 新节点的每个指针都是对下一层的搜索，不存在则新建，存在则直接返回映射对
        if (mapping.find(head) == mapping.end())
        {
            mapping[head] = new RandomListNode(head->label);
            mapping[head]->next = copyRandomList(head->next);
            mapping[head]->random = copyRandomList(head->random);
        }
        return mapping[head];
    }

问题二：

Clone Graph

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

方法一：BFS

    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return NULL;
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> mapping;
        mapping[node] = new UndirectedGraphNode(node->label);
        queue<UndirectedGraphNode*> que;
        que.push(node);
        while(!que.empty())
        {
            UndirectedGraphNode* temp = que.front();
            que.pop();
            for (int i = 0; i < temp->neighbors.size(); ++i)
            {
                if (mapping.find(temp->neighbors[i]) == mapping.end())
                {
                    mapping[temp->neighbors[i]] = new UndirectedGraphNode(temp->neighbors[i]->label);
                    que.push(temp->neighbors[i]);
                }
                mapping[temp]->neighbors.push_back(mapping[temp->neighbors[i]]);
            }
        }
        return mapping[node];
    }

方法二：DFS

    unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> mapping;
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return NULL;
        if (mapping.find(node) == mapping.end())
        {
            mapping[node] = new UndirectedGraphNode(node->label);
            for (int i = 0; i < node->neighbors.size(); ++i)
                mapping[node]->neighbors.push_back(cloneGraph(node->neighbors[i]));
        }
        return mapping[node];
    }

总结：

1、以上两种方法都用到了相同的思路，针对结构复杂的数据进行深度复制时采用了映射关系的unordered_map，从原结构指针索引新结构指针，映射关系为

Old List    --map-->    New List
node                    map[node]
head                    map[head]

2、该方法适用于数据节点中有随机指针（Random Pointer）的情况。

附原UP主代码地址：https://leetcode.com/discuss/29710/bfs-and-dfs-with-hash-unordered_map-in-c