Clone Graph DFS&BFS 图的复制

思路：

方法一：DFS，要保存一个集合来判断哪些节点已经复制过了，这里使用了unordered_map 来看集合中是否已经有了某个节点（key）。

/** * Definition for undirected graph. * struct UndirectedGraphNode { *     int label; *     vector<UndirectedGraphNode *> neighbors; *     UndirectedGraphNode(int x) : label(x) {}; * }; */class Solution {private:    UndirectedGraphNode *clone(UndirectedGraphNode *node, unordered_map<const UndirectedGraphNode *, UndirectedGraphNode *> &copy) {        if(copy.find(node) != copy.end()) {            return copy[node];        }        UndirectedGraphNode *new_node = new UndirectedGraphNode(node->label);        copy[node] = new_node;        for(auto nnr : node->neighbors) {            new_node->neighbors.push_back(clone(nnr, copy));        }        return new_node;    }public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        if(node == nullptr) return nullptr;        unordered_map<const UndirectedGraphNode *, UndirectedGraphNode *> copy;        clone(node, copy);        return copy[node];    }};

方法二：BFS，注意自环的情况。

/** * Definition for undirected graph. * struct UndirectedGraphNode { *     int label; *     vector<UndirectedGraphNode *> neighbors; *     UndirectedGraphNode(int x) : label(x) {}; * }; */class Solution {public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        if(node == nullptr) return nullptr;         queue<UndirectedGraphNode*> q;         q.push(node);         //judge hashmap         unordered_map<const UndirectedGraphNode *, UndirectedGraphNode *> copy;         UndirectedGraphNode *new_node = new UndirectedGraphNode(node->label);         copy[node] =  new_node;         while(!q.empty()) {             const UndirectedGraphNode *cur = q.front();             q.pop();             for(auto nnr : cur->neighbors) {                 if(copy.find(nnr) != copy.end()) {                     copy[cur]->neighbors.push_back(copy[nnr]);//self-circle                 }else {                     UndirectedGraphNode *new_node = new UndirectedGraphNode(nnr->label);                     copy[nnr] = new_node;                     copy[cur]->neighbors.push_back(new_node);                     q.push(nnr);                 }             }         }         return copy[node];    }};