一个例子，关于航班线路的深度优先搜索

java 代码，摘自《java 编程艺术》

/**
* 航班信息类
* 用于存放航班线路
* @author shiyan
*
*/
public class FlightInfo {
String from;//出发城市
String to;//目的城市
int distance;//距离
boolean skip;//回退标志
public FlightInfo(String f,String t,int d){
this.from=f;
this.to=t;
this.distance=d;
skip=false;
}
}



import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Stack;

/**
* 深度优先搜索
* @author shiyan
*
*/
public class Depth {
final int Max=100;
FlightInfo flights[]=new FlightInfo[Max];//航班信息
int numFlights=0;//实际航班个数
Stack btStack=new Stack();//回退标志
public static void main(String[] args){
String to,from;
Depth ob=new Depth();
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
ob.setup();
try{
System.out.println("From? ");
from=br.readLine();
System.out.print("To? ");
to=br.readLine();

ob.isFlight(from, to);
if(ob.btStack.size()!=0)
ob.route(to);
}catch(IOException e){
System.out.println("Error on input.");
}
}
public    void setup(){
addFlight("纽约","芝加哥", 900);
addFlight("芝加哥","丹佛", 1000);
addFlight("纽约","多伦多", 500);
addFlight("多伦多","卡尔加里", 1800);
addFlight("纽约","丹佛", 1700);
addFlight("多伦多","洛杉机", 2500);
addFlight("多伦多","芝加哥", 500);
addFlight("丹佛","乌儿巴纳", 1000);
addFlight("丹佛","休斯顿", 1000);
addFlight("休斯顿","洛杉机", 1500);
addFlight("丹佛","洛杉机", 1000);
}

public void addFlight(String from,String to,int dist){
if(numFlights<Max){
flights[numFlights]=new FlightInfo(from,to,dist);
numFlights++;
}else 
System.out.println("Flight database full.");
}
/**
* 确定两个城市之间是否有航班，有则返回距离，没有则返回0
* @param from
* @param to
* @return
*/
public int match(String from,String to){
for(FlightInfo flight:flights){
if(flight!=null){
if(flight.from.equals(from) && flight.to.equals(to) && !flight.skip){
flight.skip=true;//避免再次使用
return flight.distance;
}
}
}
/*for(int i=0;i<numFlights;i++){
if(flights[i].from.equals(from) && flights[i].to.equals(to) && !flights[i].skip){
flights[i].skip=true;
return flights[i].distance;
}
}*/
return 0;
}

/**
* 查询from有没有到其他任何城市的航班
* @param from
* @return
*/
public FlightInfo find(String from){
for(FlightInfo flight:flights){
if(flight!=null){
if(flight.from.equals(from) && !flight.skip){
FlightInfo f=new FlightInfo(flight.from,flight.to,flight.distance);
flight.skip=true;//避免重复使用
return f;
}
}
}
return null;
}

/**
* 查询两个城市之间线路
* @param from
* @param to
*/
public void isFlight(String from,String to){
int dist;
FlightInfo f;
dist=match(from,to);
if(dist!=0){//有直达
btStack.push(new FlightInfo(from,to,dist));
return;
}
f=find(from);
if(f!=null){
btStack.push(new FlightInfo(from,to,f.distance));
isFlight(f.to,to);
}else if(btStack.size()>0){
//回退，尝试其它路径
f=(FlightInfo) btStack.pop();
isFlight(f.from,f.to);
}
}

/**
* 显示路径和总长度
* @param to
*/
public void route(String to){
Stack rev=new Stack();
int dist=0;
FlightInfo f;
int num=btStack.size();

//反转btStack(里面的路径是相反的，栈的顶部保存的是最后一个航班信息，底部是第一个航班信息)，从起点到终点显示路径将路径压栈rev中
for(int i=0;i<num;i++){
rev.push(btStack.pop());
}

for(int i=0;i<num;i++){
f=(FlightInfo)rev.pop();
System.out.print(f.from+" to ");
dist+=f.distance;
}
System.out.println(to);
System.out.println("Distance is "+dist);
}

}