Clone Graph DFS&BFS 图的复制

最新推荐文章于 2022-02-01 15:26:15 发布

原创最新推荐文章于 2022-02-01 15:26:15 发布 · 489 阅读

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本文探讨了使用深度优先搜索（DFS）和广度优先搜索（BFS）在无向图复制过程中的应用，详细介绍了算法实现步骤及注意事项，特别关注了自环情况的处理。

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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];
    }
};