[leetcode] 133.Clone Graph

最新推荐文章于 2024-01-21 17:12:09 发布

白雪忆青竹

最新推荐文章于 2024-01-21 17:12:09 发布

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分类专栏： leetcode 文章标签：图深度优先搜索

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本文详细介绍了如何使用深度优先搜索算法克隆无向树，包括数据结构定义、核心思路、实现细节以及代码示例。

题目：
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:

   1
  / \
 /   \
0 --- 2
     / \
     \_/

题意：
克隆一棵无向树。
思路：
对于任何一个边，(i,j),i的相邻节点有j，j的相邻节点有i。由于需要复制每一个节点，所以需要new出每一个节点，但是由于任和边都会被访问两次，(i,j),(j,i),比如一开始先复制出i节点，然后需要递归复制与i相邻的节点j，复制j节点的时候需要去复制j的相邻节点，由于i节点之前已经复制过，所以此处不需要再复制i节点。我采用了unordered_map来存放已经复制的节点，由于这道题给每个节点一个标记了，所以可以完美的使用map来保存（label值，节点）这样的键值对。
采用的是深度优先算法。
详细代码请参考如下：

/**
 * 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 == NULL)return NULL;
        UndirectedGraphNode *root = NULL;
        cloneGraphRecur(root, node);
        return root;
    }
    void cloneGraphRecur(UndirectedGraphNode *&root, UndirectedGraphNode *&node) {
        root = new UndirectedGraphNode(node->label);
        existNodes[node->label] = root;
        for(auto neighbor:node->neighbors) {
            if(existNodes.find(neighbor->label) == existNodes.end()){
                UndirectedGraphNode *temp = NULL;
                cloneGraphRecur(temp, neighbor);
                root->neighbors.push_back(temp);
            }
            else root->neighbors.push_back(existNodes[neighbor->label]);
        }
    }
    private:
    unordered_map<int,UndirectedGraphNode*> existNodes;
};