Tuesday, February 3, 2015

LeetCode [133] Clone Graph

 133. Clone Graph

Medium

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.
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//C++: method1 80ms DFS
/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
    map<int, UndirectedGraphNode*> hash;
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(!node) return NULL;
        UndirectedGraphNode *newNode = new UndirectedGraphNode(node->label);
        hash[node->label] = newNode;
        for(auto n:node->neighbors){
            if(hash.count(n->label)==0){
                cloneGraph(n);
            }
            newNode->neighbors.push_back(hash[n->label]);
        }
        return newNode;
    }
};
]]></script>


//C++: method2 76ms
/**
 * 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 node;
        unordered_map<int, UndirectedGraphNode *> hash;
        UndirectedGraphNode * newNode = new UndirectedGraphNode(node->label);
        hash[node->label] = newNode;
        queue<UndirectedGraphNode *> que;
        que.push(node);

        while(!que.empty()){
            UndirectedGraphNode * t = que.front();
            que.pop();
            for(auto nb:t->neighbors){
                UndirectedGraphNode *newNb = NULL;
                if(hash.count(nb->label)==0){
                    newNb = new UndirectedGraphNode(nb->label);
                    hash[nb->label] = newNb;
                    que.push(nb);
                }
                hash[t->label]->neighbors.push_back(hash[nb->label]);
            }
        }

        return newNode;
    }
};


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

class Solution {
    Map<Integer, Node> map = new HashMap<>();
    public Node cloneGraph(Node node) {
        if(node==null) return null;
        if(map.containsKey(node.val)) return map.get(node.val);
        
        Node newNode = new Node(node.val);
        map.put(node.val, newNode);
        for(Node n : node.neighbors){
            newNode.neighbors.add(cloneGraph(n));
        }
        
        return newNode;
    }
}
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