133. Clone Graph

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

Each node in the graph contains a val (int) and a list (List[Node]) of its neighbors.

class Node {
    public int val;
    public List<Node> neighbors;
}
 

Test case format:

For simplicity sake, each node's value is the same as the node's index (1-indexed). For example, the first node with val = 1, the second node with val = 2, and so on. The graph is represented in the test case using an adjacency list.

Adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

 

Example 1:


Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
Output: [[2,4],[1,3],[2,4],[1,3]]
Explanation: There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
Example 2:


Input: adjList = [[]]
Output: [[]]
Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.
Example 3:

Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.
Example 4:


Input: adjList = [[2],[1]]
Output: [[2],[1]]
 

Constraints:

1 <= Node.val <= 100
Node.val is unique for each node.
Number of Nodes will not exceed 100.
There is no repeated edges and no self-loops in the graph.
The Graph is connected and all nodes can be visited starting from the given node.

这题让我们深拷贝一个无向图。数据结构中每个节点的值给出了，并且也给出了邻接节点。

我们从根节点开始遍历，假设该节点没有被拷贝过，则拷贝，然后遍历邻居，也按该规则，然后将该拷贝的邻居节点接到拷贝过的根节点上即可。

// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> neighbors;
    Node() {
        val = 0;
        neighbors = vector<Node*>();
    }
    Node(int _val) {
        val = _val;
        neighbors = vector<Node*>();
    }
    Node(int _val, vector<Node*> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }
};


class CloneGraph : public Solution {
public:
    void Exec() {
        
    }

    Node* cloneGraph(Node* node) {
        if (nullptr == node) return nullptr;
        unordered_map<Node*, Node*> copyMap {{node, new Node(node->val)}};
        deque<Node *> nodes;
        nodes.push_back(node);

        while (!nodes.empty()) {
            Node *cur = nodes.back();
            nodes.pop_back();

            for (int i = 0; i < cur->neighbors.size(); i++) {
                Node *neigh = cur->neighbors[i];
                auto it = copyMap.find(neigh);
                Node *cnode = nullptr;
                if (copyMap.end() == it) {
                    cnode = new Node(neigh->val);
                    nodes.push_back(neigh);
                    copyMap[neigh] = cnode;
                } else {
                    cnode = it->second;
                }
                copyMap[cur]->neighbors.push_back(cnode);
            }
        }
        return copyMap[node];
    }
};