133. Clone Graph

最新推荐文章于 2017-12-20 10:19:06 发布

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最新推荐文章于 2017-12-20 10:19:06 发布

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分类专栏： Leetcode

本文链接：https://blog.youkuaiyun.com/gcola007/article/details/78584948

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本文探讨了如何通过深度优先搜索(DFS)和广度优先搜索(BFS)来克隆无向图，并解决了节点重复拷贝的问题。使用unordered_map来跟踪已拷贝的节点，确保每个节点仅被复制一次。

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

OJ's undirected graph serialization:

Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.

As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

拷贝一个图，最先想到的就是DFS与BFS了，但是这个题目的一个关键问题是

如果图是 1--2 这种样子，拷贝1，拷贝邻居2，拷贝2 这个时候出现了重复

所以利用unordered_map处理这个重复十分关键

BFS:

class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return NULL;
        UndirectedGraphNode* copy = new UndirectedGraphNode(node -> label);
        mp[node] = copy;
        queue<UndirectedGraphNode*> toVisit;
        toVisit.push(node);
        while (!toVisit.empty()) {
            UndirectedGraphNode* cur = toVisit.front();
            toVisit.pop();
            for (UndirectedGraphNode* neigh : cur -> neighbors) {
                if (mp.find(neigh) == mp.end()) {
                    UndirectedGraphNode* neigh_copy = new UndirectedGraphNode(neigh -> label);
                    mp[neigh] = neigh_copy;
                    toVisit.push(neigh);
                }
                mp[cur] -> neighbors.push_back(mp[neigh]);
            }
        }
        return copy; 
    }
private:
    unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> mp;
};

DFS:

/**
 * 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) return nullptr;
        if(m.find(node)==m.end()){
            m[node]=new UndirectedGraphNode(node->label);
            for(UndirectedGraphNode* neigh:node->neighbors)
                m[node]->neighbors.push_back(cloneGraph(neigh));
        }
        return m[node];
    }
private:
    unordered_map<UndirectedGraphNode*,UndirectedGraphNode*> m;
};