描述
克隆一張無(wú)向圖，圖中的每個(gè)節(jié)點(diǎn)包含一個(gè) label 和一個(gè)列表 neighbors。數(shù)據(jù)中如何表示一個(gè)無(wú)向圖？http://www.lintcode.com/help/graph/你的程序需要返回一個(gè)經(jīng)過(guò)深度拷貝的新圖。這個(gè)新圖和原圖具有同樣的結(jié)構(gòu)，并且對(duì)新圖的任何改動(dòng)不會(huì)對(duì)原圖造成任何影響。
樣例
比如，序列化圖 {0,1,2#1,2#2,2} 共有三個(gè)節(jié)點(diǎn), 因此包含兩個(gè)個(gè)分隔符#。
第一個(gè)節(jié)點(diǎn)label為0，存在邊從節(jié)點(diǎn)0鏈接到節(jié)點(diǎn)1和節(jié)點(diǎn)2
第二個(gè)節(jié)點(diǎn)label為1，存在邊從節(jié)點(diǎn)1連接到節(jié)點(diǎn)2
第三個(gè)節(jié)點(diǎn)label為2，存在邊從節(jié)點(diǎn)2連接到節(jié)點(diǎn)2(本身),從而形成自環(huán)。
我們能看到如下的圖：
1
/ \
/ \
0 --- 2
/ \
\_/
代碼
- 3steps
/**
* Definition for undirected graph.
* class UndirectedGraphNode {
* int label;
* ArrayList<UndirectedGraphNode> neighbors;
* UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
public class Solution {
/**
* @param node: A undirected graph node
* @return: A undirected graph node
*/
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null) {
return node;
}
// use bfs algorithm to traverse the graph and get all nodes.
ArrayList<UndirectedGraphNode> nodes = getNodes(node);
// copy nodes, store the old->new mapping information in a hash map
HashMap<UndirectedGraphNode, UndirectedGraphNode> mapping = new HashMap<>();
for (UndirectedGraphNode n : nodes) {
// 創(chuàng)建hashmap將原圖和新圖之間結(jié)點(diǎn)對(duì)應(yīng)關(guān)系存在hashmap中
mapping.put(n, new UndirectedGraphNode(n.label));
}
// copy neighbors(edges)
for (UndirectedGraphNode n : nodes) {
// 復(fù)制的新的結(jié)點(diǎn),不能寫(xiě)newNode = n這樣復(fù)制的是引用，我們需要的是deep copy
UndirectedGraphNode newNode = mapping.get(n);
// neighbors是定義好的存儲(chǔ)整型下標(biāo)的數(shù)組
for (UndirectedGraphNode neighbor : n.neighbors) {
// 復(fù)制相鄰結(jié)點(diǎn)，復(fù)制相鄰結(jié)點(diǎn)和復(fù)制的結(jié)點(diǎn)建立邊的關(guān)系
UndirectedGraphNode newNeighbor = mapping.get(neighbor);
newNode.neighbors.add(newNeighbor);
}
}
// 從輸入的結(jié)點(diǎn)開(kāi)始逐漸返回圖中每個(gè)結(jié)點(diǎn)對(duì)應(yīng)的信息
return mapping.get(node);
}
// 用bfs由點(diǎn)到面得到所有結(jié)點(diǎn)信息，返回一個(gè)包含所有結(jié)點(diǎn)的數(shù)組
private ArrayList<UndirectedGraphNode> getNodes(UndirectedGraphNode node) {
Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
// HashSet不允許有相同元素，如果b已是集合中元素，再執(zhí)行set.add(b)無(wú)效
HashSet<UndirectedGraphNode> set = new HashSet<>();
queue.offer(node);
set.add(node);
// bfs利用隊(duì)列來(lái)控制遍歷圖中結(jié)點(diǎn)的順序
while (!queue.isEmpty()) {
UndirectedGraphNode head = queue.poll();
for (UndirectedGraphNode neighbor : head.neighbors) {
if(!set.contains(neighbor)){
set.add(neighbor);
queue.offer(neighbor);
}
}
}
// 所有結(jié)點(diǎn)都已添加到 set，此處用深度拷貝是因?yàn)橥膺呉肁rrayList，而此處是hashset
return new ArrayList<UndirectedGraphNode>(set);
}
}
- two steps
/**
* Definition for undirected graph.
* class UndirectedGraphNode {
* int label;
* ArrayList<UndirectedGraphNode> neighbors;
* UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
public class Solution {
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null) {
return null;
}
ArrayList<UndirectedGraphNode> nodes = new ArrayList<UndirectedGraphNode>();
HashMap<UndirectedGraphNode, UndirectedGraphNode> map
= new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
// clone nodes
nodes.add(node);
map.put(node, new UndirectedGraphNode(node.label));
int start = 0;
while (start < nodes.size()) {
UndirectedGraphNode head = nodes.get(start++);
for (int i = 0; i < head.neighbors.size(); i++) {
UndirectedGraphNode neighbor = head.neighbors.get(i);
if (!map.containsKey(neighbor)) {
map.put(neighbor, new UndirectedGraphNode(neighbor.label));
nodes.add(neighbor);
}
}
}
// clone neighbors
for (int i = 0; i < nodes.size(); i++) {
UndirectedGraphNode newNode = map.get(nodes.get(i));
for (int j = 0; j < nodes.get(i).neighbors.size(); j++) {
newNode.neighbors.add(map.get(nodes.get(i).neighbors.get(j)));
}
}
return map.get(node);
}
}
- Non-Recursion DFS
/**
* Definition for undirected graph.
* class UndirectedGraphNode {
* int label;
* ArrayList<UndirectedGraphNode> neighbors;
* UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
class StackElement {
public UndirectedGraphNode node;
public int neighborIndex;
public StackElement(UndirectedGraphNode node, int neighborIndex) {
this.node = node;
this.neighborIndex = neighborIndex;
}
}
public class Solution {
/**
* @param node: A undirected graph node
* @return: A undirected graph node
*/
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null) {
return node;
}
// use dfs algorithm to traverse the graph and get all nodes.
ArrayList<UndirectedGraphNode> nodes = getNodes(node);
// copy nodes, store the old->new mapping information in a hash map
HashMap<UndirectedGraphNode, UndirectedGraphNode> mapping = new HashMap<>();
for (UndirectedGraphNode n : nodes) {
mapping.put(n, new UndirectedGraphNode(n.label));
}
// copy neighbors(edges)
for (UndirectedGraphNode n : nodes) {
UndirectedGraphNode newNode = mapping.get(n);
for (UndirectedGraphNode neighbor : n.neighbors) {
UndirectedGraphNode newNeighbor = mapping.get(neighbor);
newNode.neighbors.add(newNeighbor);
}
}
return mapping.get(node);
}
private ArrayList<UndirectedGraphNode> getNodes(UndirectedGraphNode node) {
Stack<StackElement> stack = new Stack<StackElement>();
HashSet<UndirectedGraphNode> set = new HashSet<>();
stack.push(new StackElement(node, -1));
set.add(node);
while (!stack.isEmpty()) {
StackElement current = stack.peek();
current.neighborIndex++;
// there is no more neighbor to traverse for the current node
if (current.neighborIndex == current.node.neighbors.size()) {
stack.pop();
continue;
}
UndirectedGraphNode neighbor = current.node.neighbors.get(
current.neighborIndex
);
// check if we visited this neighbor before
if (set.contains(neighbor)) {
continue;
}
stack.push(new StackElement(neighbor, -1));
set.add(neighbor);
}
return new ArrayList<UndirectedGraphNode>(set);
}
}