LeetCode Clone Graph

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class Solution {public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        UndirectedGraphNode *clone = dfs(node);        dfs_clear(node);        return clone;    }        UndirectedGraphNode *dfs(UndirectedGraphNode *orgin) {        if (orgin == NULL) return NULL;        UndirectedGraphNode *clone = get_clone_node(orgin);        if (clone != NULL) return clone;        // cout<<"cloning node :"<<orgin->label<<endl;        int olen = orgin->neighbors.size();                clone = add_clone_node(orgin);                for (int i=0; i<olen; i++) {            UndirectedGraphNode *nb = orgin->neighbors[i];            clone->neighbors.push_back(dfs(nb));        }        return clone;    }        void dfs_clear(UndirectedGraphNode *node) {        UndirectedGraphNode *clone = get_clone_node(node);        if (clone == NULL) return;        // cout<<"clear node: "<<node->label<<endl;        del_clone_node(node);                int len = node->neighbors.size();                for (int i=0; i<len; i++) {            dfs_clear(node->neighbors[i]);        }    }        UndirectedGraphNode *get_clone_node(UndirectedGraphNode *node) {        int len;        // cout<<"get info of cloned node : "<<node->label<<endl;        if (node == NULL || (len = node->neighbors.size()) < 2            || node->neighbors[len - 2] != NULL) return NULL;        return node->neighbors[len - 1];    }        UndirectedGraphNode *add_clone_node(UndirectedGraphNode *node) {        if (node == NULL) return NULL;        // cout<<"append link for cloned node: "<<node->label<<endl;        node->neighbors.push_back(NULL);        node->neighbors.push_back(new UndirectedGraphNode(node->label));        return node->neighbors.back();    }        void del_clone_node(UndirectedGraphNode *node) {        if (get_clone_node(node) == NULL) return;        // cout<<"del clone link for node:"<<node->label<<endl;        node->neighbors.pop_back(); // cloned node addr        node->neighbors.pop_back(); // null    }};

dfs掃描複製，通過在neighbor數組中加入NULL指標來標記已複製與未複製的節點，同時在NULL項後儲存該節點對應的複製節點，最後將原有節點還原。240ms

類似的可以用一個hash表來儲存新節點地址與對應老節點的對應關係，同時進行串連關係的複製。當然兩種方法的dfs可以改成bfs，防止棧溢出。

class Solution {private:    unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> o2n;public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        o2n.clear();        UndirectedGraphNode *clone = dfs(node);        return clone;    }        UndirectedGraphNode *dfs(UndirectedGraphNode *node) {        if (node == NULL) return NULL;        unordered_map<UndirectedGraphNode *, UndirectedGraphNode *>::iterator iter = o2n.find(node);        if (iter != o2n.end()) return iter->second;                UndirectedGraphNode *clone = new UndirectedGraphNode(node->label);        o2n.insert(make_pair(node, clone));                int len = node->neighbors.size();                for (int i=0; i<len; i++) {            clone->neighbors.push_back(dfs(node->neighbors[i]));        }        return clone;    }};