我正在做一个家庭作业项目，在那里我从一个文件中读取一个连接站列表，并创建一个格式（key = String station，value = ArrayList连接站）的散列图到目前为止一切都很好。
然后，用户可以选择一个本地站，此时我正在尝试创建一个树来代表家中所有可访问的站点。树可以看起来像：
HomeStation
/ \
station1 station2
/ | \
station3 station4 station 5
但我无法理解如何将这些电台添加到除了根及其子节点之外的树上。所以任何人都可以给我一些关于我应该做什么/看什么的指示。
到目前为止我的TreeNode类：
/**
* TreeNode class
* Represents a N-ary tree node
* Uses ArrayList to hold the children.
* @author Ásta B. Hansen (11038973)
*
*/
public class TreeNode {
private String station;
private TreeNode parent;
private List<TreeNode> children;
/**
* Constructor
* @param station - the station to be stored in the node
*/
public TreeNode(String station) {
this.station = station;
parent = null;
children = new ArrayList<TreeNode>(); //Empty list of children
}
/**
* Sets the station in this node
* @param station - the station to be stored
*/
public void setStation(String station) {
this.station = station;
}
/**
* Returns the station in this node
* @return station
*/
public String getStation() {
return station;
}
/**
* Sets the parent of this node
* @param parent - the parent node
*/
public void setParent(TreeNode parent) {
this.parent = parent;
}
/**
* Returns the parent of this node or null if there is no parent
* @return parent
*/
public TreeNode getParent() {
return parent;
}
/**
* Adds a single child to this node
* @param newChild - the child node to be added
*/
public void addChild(TreeNode newChild) {
children.add(newChild);
newChild.setParent(this);
}
/**
* Returns a list of the children of this node
* @return children - the children of the node
*/
public List<TreeNode> getChildren() {
return children;
}
/**
* Returns the number of children this node has
* @return number of children
*/
public int getNumberOfChildren() {
return children.size();
}
/**
* Indicates whether this is a leaf node (has no children)
* @return true if the node has no children
*/
public boolean isLeaf() {
return children.isEmpty();
}
/**
* TODO print preOrder tree
*/
public void printPreOrder() {
}
/**
* TODO print postOrder tree
*/
public void printPostOrder() {
}
}
在Main：
private static void selectHome() {
if(network != null) {
System.out.print("Please enter the name of the home station> ");
homeStation = scan.next();
if(!network.hasStation(homeStation)) { //if station does not exist
System.out.println("There is no station by the name " + homeStation + "\n");
homeStation = null;
} else {
//create the tree with homeStation as root
createTree(homeStation);
}
} else {
System.out.println("You must load a network file before choosing a home station.\n");
}
}
private static void createTree(String homeStation) {
root = new TreeNode(homeStation); //create root node with home station
//TODO Construct the tree
//get list of connecting stations from network (string[])
//and add the stations as children to the root node
for(String stationName : network.getConnections(homeStation)) {
TreeNode child = new TreeNode(stationName);
root.addChild(child);
//then for every child of the tree get connecting stations from network
//and add those as children of the child.
//TODO as long as a station doesn't already exist in the tree.
}
}
修改 电台输入文件
Connection: Rame Penlee
Connection: Penlee Rame
Connection: Rame Millbrook
Connection: Millbrook Cawsand
Connection: Cawsand Kingsand
Connection: Kingsand Rame
Connection: Millbrook Treninnow
Connection: Treninnow Millbrook
Connection: Millbrook Antony
Connection: Antony Polbathic
Connection: Polbathic Rame
答案 0 :(得分：7)
这是一个基本问题（我猜这必须是某种功课），我认为一个简单的递归可以帮助你解决它。
创建一个查找节点的每个子节点的函数，并在每个子节点上调用此函数：
private static void addNodesRecursive(TreeNode node) {
for(String stationName : network.getConnections(node)) {
TreeNode child = new TreeNode(stationName);
node.addChild(child);
addNodesRecursive(child);
}
}
仅当我们制作的图表为DAG时才有效。如果图形中有任何周期（即使是双向边缘），它将失败。
它会失败，因为我们之前尚未存储节点是否已添加到我们的图表中。父母将与孩子相连，反之亦然，他们将作为邻居无限地加入。
你可以做的是：制作一个存储已添加内容的列表。
private static void addNodesRecursive(TreeNode node, List<TreeNode> addedList) {
for(String stationName : network.getConnections(node)) {
TreeNode child = new TreeNode(stationName);
node.addChild(child);
addedList.add(child);
addNodesRecursive(child, addedList);
}
}
如果新节点不在添加的列表上，则只添加新节点：
private static void addNodesRecursive(TreeNode node, List<String> addedList) {
for(String stationName : network.getConnections(node)) {
if (!addedList.contains(stationName)) {
TreeNode child = new TreeNode(stationName);
node.addChild(child);
addedList.add(child);
addNodesRecursive(child, addedList);
}
}
}
您只需要在根节点上调用它，因此createTree将是：
private static void createTree(String homeStation) {
root = new TreeNode(homeStation);
List<String> addedList = new ArrayList<String>();
addedList.add(homeStation);
addNodesRecursive(root, addedList);
}
BAM你完成了。调用createTree将从根开始创建树。
P.S。我正在写这个，我没有尝试我的代码，我的Java也有点生疏，所以你可以指望它包含语法错误（就像我已经用小s纠正了我的所有字符串到大写S ）。
修改：
如果您有任何计划程序的计划，能够自己找出递归问题非常重要。关于如何找出递归的东西的一点帮助。
至少我是这样做的（并且在回答这个问题的时候也这样做了:)）。