LEEDCODE: Clone Graph_leedcoder-优快云博客

本文链接：https://blog.youkuaiyun.com/anyicheng2015/article/details/42470527

本文介绍了一种高效的克隆无向图算法，通过使用哈希映射避免重复复制节点，确保每个节点仅被克隆一次。算法首先检查输入节点是否为空，然后利用递归方式遍历并复制所有相邻节点。

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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:

这题的重点是不要重复复制，所以我用map对每个节点做了映射。

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    map<UndirectedGraphNode *, UndirectedGraphNode *> themap;
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(node == NULL)    return node;
        themap.clear();
        return cloneGraphInternal(node);
    }
    UndirectedGraphNode *cloneGraphInternal(UndirectedGraphNode *node) {
        UndirectedGraphNode *ugn = new UndirectedGraphNode(node->label);
        themap[node] = ugn;
        for(int ii = 0; ii < node->neighbors.size(); ii ++) {
            if(themap.count(node->neighbors[ii]) > 0) {
                ugn->neighbors.push_back(themap[node->neighbors[ii]]);
            }
            else {
                UndirectedGraphNode *ugn2 = cloneGraphInternal(node->neighbors[ii]);
                themap[node->neighbors[ii]] = ugn2;
                ugn->neighbors.push_back(themap[node->neighbors[ii]]);
            }
        }
        return ugn;
    }
};