Mega Code Archive
Find the lost keys
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/*
*
* Chapter 10 - AI-Based Problem Solving The Art of Java by Herbert Schildt and
* James Holmes McGraw-Hill/Osborne 2003
*/
import java.util.Stack;
//Room information.
class RoomInfo {
String from;
String to;
boolean skip;
RoomInfo(String f, String t) {
from = f;
to = t;
skip = false;
}
}
public class Keys {
final int MAX = 100;
// This array holds the room information.
RoomInfo room[] = new RoomInfo[MAX];
int numRooms = 0; // number of rooms
Stack btStack = new Stack(); // backtrack stack
public static void main(String args[]) {
String to, from;
Keys ob = new Keys();
ob.setup();
from = "front_door";
to = "keys";
ob.iskeys(from, to);
if (ob.btStack.size() != 0)
ob.route(to);
}
// Initialize the room database.
void setup() {
addRoom("front_door", "lr");
addRoom("lr", "bath");
addRoom("lr", "hall");
addRoom("hall", "bd1");
addRoom("hall", "bd2");
addRoom("hall", "mb");
addRoom("lr", "kitchen");
addRoom("kitchen", "keys");
}
// Put rooms into the database.
void addRoom(String from, String to) {
if (numRooms < MAX) {
room[numRooms] = new RoomInfo(from, to);
numRooms++;
} else
System.out.println("Room database full.\n");
}
// Show the route.
void route(String to) {
Stack rev = new Stack();
RoomInfo r;
int num = btStack.size();
// Reverse the stack to display path.
for (int i = 0; i < num; i++)
rev.push(btStack.pop());
for (int i = 0; i < num; i++) {
r = (RoomInfo) rev.pop();
System.out.print(r.from + " to ");
}
System.out.println(to);
}
/*
* If there is a path between from and to, return true, otherwise return
* false.
*/
boolean match(String from, String to) {
for (int i = numRooms - 1; i > -1; i--) {
if (room[i].from.equals(from) && room[i].to.equals(to)
&& !room[i].skip) {
room[i].skip = true; // prevent reuse
return true;
}
}
return false; // not found
}
// Given from, find any path.
RoomInfo find(String from) {
for (int i = 0; i < numRooms; i++) {
if (room[i].from.equals(from) && !room[i].skip) {
RoomInfo r = new RoomInfo(room[i].from, room[i].to);
room[i].skip = true; // prevent reuse
return r;
}
}
return null;
}
// Determine if there is a path between from and to.
void iskeys(String from, String to) {
int dist;
RoomInfo r;
// See if at destination.
if (match(from, to)) {
btStack.push(new RoomInfo(from, to));
return;
}
// Try another connection.
r = find(from);
if (r != null) {
btStack.push(new RoomInfo(from, to));
iskeys(r.to, to);
} else if (btStack.size() > 0) {
// Backtrack and try another connection.
r = (RoomInfo) btStack.pop();
iskeys(r.from, r.to);
}
}
}
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