133. Clone Graph(Leetcode每日一题-2020.08.12)

Problem

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.

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.

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.

Example1

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).

Example2

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.

Example3

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

Example4

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

Solution

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

class Solution {
public:
    Node* cloneGraph(Node* node) {
        if (!node) return NULL;

        unordered_map<Node *,Node *> hash_table;
        queue<Node *> q;
        q.push(node);

        while(!q.empty())
        {
            Node* tmp = q.front();
            q.pop();
            if(hash_table.count(tmp))
                continue;
        
            Node * tmp_copy = new Node(tmp->val);
            hash_table[tmp] = tmp_copy;
    
            for(auto nbr:tmp->neighbors)
            {
                q.push(nbr);
            }
        }

        for (auto [s, d]: hash_table) {
            for (auto ver: s->neighbors)
                d->neighbors.push_back(hash_table[ver]);
        }


        return hash_table[node];


        
    }
};