LeetCode——复制图

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http://articles.leetcode.com/2012/05/clone-graph-part-i.html

BFS方法遍历图。为了防止重复遍历，使用hashmap，key为原图的node，value为新图的node。

我没有看原文的算法实现先是自己想了然后写上去。这样的过程中我碰到了一些问题。比如说什么时候创建新的节点？是在while的开始，还是在遍历相邻节点的时候？这点很重要。

实现：

package com.song.algorithm;import java.util.ArrayList;import java.util.HashMap;import java.util.HashSet;import java.util.LinkedList;import java.util.List;import java.util.Queue;public class Image {public static class Node {public int data;public List<Node> neighbors;}public Node head;public static Image copy(Image image) {Queue<Node> queue = new LinkedList<Node>();if (image.head == null) {return null;}Image cp = new Image();HashMap<Node, Node> map = new HashMap<Node, Node>();Node newHead = new Node();newHead.data = image.head.data;cp.head = newHead;map.put(image.head, newHead);queue.add(image.head);while (!queue.isEmpty()) {Node node = queue.remove();Node cnode = map.get(node);if (node.neighbors != null) {List<Node> cnodeNeighbors = new ArrayList<Node>();cnode.neighbors = cnodeNeighbors;for (Node n : node.neighbors) {if (map.get(n) == null) {Node newNode = new Node();newNode.data = n.data;map.put(n, newNode);cnodeNeighbors.add(newNode);queue.add(n);} else {cnodeNeighbors.add(map.get(n));}}}}return cp;}public static void iterate(Image image) {HashSet<Node> set = new HashSet<Node>();set.add(image.head);Queue<Node> queue = new LinkedList<Node>();queue.add(image.head);while (!queue.isEmpty()) {Node node = queue.remove();System.out.print(node.data + " ");if (node.neighbors != null) {for (Node n : node.neighbors) {if (!set.contains(n)) {queue.add(n);set.add(n);}}}}}public static void main(String[] args) {Image image = new Image();Node head = new Node();image.head = head;head.data = 1;ArrayList<Node> nei1 = new ArrayList<Node>();Node n2 = new Node();n2.data = 2;nei1.add(n2);head.neighbors = nei1;ArrayList<Node> nei2 = new ArrayList<Node>();Node n3 = new Node();n3.data = 3;nei2.add(n3);Node n4 = new Node();n4.data = 4;nei2.add(n4);n2.neighbors = nei2;ArrayList<Node> nei3 = new ArrayList<Node>();nei3.add(head);n4.neighbors = nei3;iterate(image);System.out.println("");Image image1 = copy(image);iterate(image1);}}

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