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LionDeer.java
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LionDeer.java
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import java.util.LinkedList;
import java.util.Scanner;
import java.util.Queue;
/*
* Author: Joseph Nuhfer
* Version: 11.30.16
*
* The program solves the n-lions and n-deer boat problem using a Java Queue.
* - There are n lions and n deer on one side of the river (the left side).
* - You want to take all of them to the other side of the river.
* - You have a boat, and you can take at most two animals at a time. (you must take at least one each trip).
* - If at any point the deer fall to below half the number of lions, the lions will eat the deer and you will fail.
* - What is the minimum number of trips it will take to take all of the animals from one side to the other?
*/
public class LionDeer {
private static int n;
private static Node[][] pred;
private static Node goal;
private static int[][] dist;
private static Queue<Node> q;
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
q = new LinkedList<Node>();
n = keyboard.nextInt();
pred = new Node[n * 2 + 2][n * 2 + 2];
dist = new int[n * 2 + 2][n * 2 + 2];
for (int i = 0; i < n * 2 + 1; i++) {
for (int j = 0; j < n * 2 + 1; j++) {
pred[i][j] = new Node(-1, -1, -1, -1, false);
dist[i][j] = Integer.MAX_VALUE;
}
}
dist[n][n] = 0;
q.add(new Node(n, n, 0, 0, false));
while (goal == null)
bfs(q.remove());
System.out.println("Yay!");
printPath(goal);
System.out.println(dist[n * 2 + 1][n * 2 + 1] + " trips required.");
}
private static void bfs(Node node) {
if (node.rightDeer == n && node.rightLions == n) {
if (node.isRightBoat)
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer + n][node.leftLions + n];
else
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer][node.leftLions];
goal = new Node(node.leftDeer, node.leftLions, node.rightDeer, node.rightLions, node.isRightBoat);
return;
}
if (((node.leftLions > node.leftDeer * 2) && node.leftDeer != 0) || ((node.rightLions > node.rightDeer * 2) && node.rightDeer != 0)) {
return;
}
if (node.isRightBoat) {
if (node.rightDeer >= 2) {
if (node.rightDeer - 2 == n && node.rightLions == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
goal = new Node(node.leftDeer + 2, node.leftLions, node.rightDeer - 2, node.rightLions, false);
return;
}
if (dist[node.leftDeer + 2][node.leftLions] == Integer.MAX_VALUE) {
pred[node.leftDeer + 2][node.leftLions] = node;
dist[node.leftDeer + 2][node.leftLions] = dist[node.leftDeer + n][node.leftLions + n] + 1;
q.add(new Node(node.leftDeer + 2, node.leftLions, node.rightDeer - 2, node.rightLions, false));
}
}
if (node.rightLions >= 2) {
if (node.rightDeer == n && node.rightLions - 2 == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
goal = new Node(node.leftDeer, node.leftLions + 2, node.rightDeer, node.rightLions - 2, false);
return;
}
if (dist[node.leftDeer][node.leftLions + 2] == Integer.MAX_VALUE) {
pred[node.leftDeer][node.leftLions + 2] = node;
dist[node.leftDeer][node.leftLions + 2] = dist[node.leftDeer + n][node.leftLions + n] + 1;
q.add(new Node(node.leftDeer, node.leftLions + 2, node.rightDeer, node.rightLions - 2, false));
}
}
if (node.rightDeer != 0 && node.rightLions != 0) {
if (node.rightDeer - 1 == n && node.rightLions - 1 == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
goal = new Node(node.leftDeer + 1, node.leftLions + 1, node.rightDeer - 1, node.rightLions - 1, false);
return;
}
if (dist[node.leftDeer + 1][node.leftLions + 1] == Integer.MAX_VALUE) {
pred[node.leftDeer + 1][node.leftLions + 1] = node;
dist[node.leftDeer + 1][node.leftLions + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
q.add(new Node(node.leftDeer + 1, node.leftLions + 1, node.rightDeer - 1, node.rightLions - 1, false));
}
}
if (node.rightDeer != 0) {
if (node.rightDeer - 1 == n && node.rightLions == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
goal = new Node(node.leftDeer + 1, node.leftLions, node.rightDeer - 1, node.rightLions, false);
return;
}
if (dist[node.leftDeer + 1][node.leftLions] == Integer.MAX_VALUE) {
pred[node.leftDeer + 1][node.leftLions] = node;
dist[node.leftDeer + 1][node.leftLions] = dist[node.leftDeer + n][node.leftLions + n] + 1;
q.add(new Node(node.leftDeer + 1, node.leftLions, node.rightDeer - 1, node.rightLions, false));
}
}
if (node.rightLions != 0) {
if (node.rightDeer == n && node.rightLions - 1 == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
goal = new Node(node.leftDeer, node.leftLions + 1, node.rightDeer, node.rightLions - 1, false);
return;
}
if (dist[node.leftDeer][node.leftLions + 1] == Integer.MAX_VALUE) {
pred[node.leftDeer][node.leftLions + 1] = node;
dist[node.leftDeer][node.leftLions + 1] = dist[node.leftDeer + n][node.leftLions + n] + 1;
q.add(new Node(node.leftDeer, node.leftLions + 1, node.rightDeer, node.rightLions - 1, false));
}
}
}
else {
if (node.leftDeer >= 2) {
if (node.rightDeer + 2 == n && node.rightLions == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer][node.leftLions] + 1;
goal = new Node(node.leftDeer - 2, node.leftLions, node.rightDeer + 2, node.rightLions, true);
return;
}
if (dist[node.leftDeer - 2 + n][node.leftLions + n] == Integer.MAX_VALUE) {
pred[node.leftDeer - 2 + n][node.leftLions + n] = node;
dist[node.leftDeer - 2 + n][node.leftLions + n] = dist[node.leftDeer][node.leftLions] + 1;
q.add(new Node(node.leftDeer - 2, node.leftLions, node.rightDeer + 2, node.rightLions, true));
}
}
if (node.leftLions >= 2) {
if (node.rightDeer == n && node.rightLions + 2 == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer][node.leftLions] + 1;
goal = new Node(node.leftDeer, node.leftLions - 2, node.rightDeer, node.rightLions + 2, true);
return;
}
if (dist[node.leftDeer + n][node.leftLions - 2 + n] == Integer.MAX_VALUE) {
pred[node.leftDeer + n][node.leftLions - 2 + n] = node;
dist[node.leftDeer + n][node.leftLions - 2 + n] = dist[node.leftDeer][node.leftLions] + 1;
q.add(new Node(node.leftDeer, node.leftLions - 2, node.rightDeer, node.rightLions + 2, true));
}
}
if (node.leftDeer != 0 && node.leftLions != 0) {
if (node.rightDeer + 1 == n && node.rightLions + 1 == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer][node.leftLions] + 1;
goal = new Node(node.leftDeer - 1, node.leftLions - 1, node.rightDeer + 1, node.rightLions + 1, true);
return;
}
if (dist[node.leftDeer - 1 + n][node.leftLions - 1 + n] == Integer.MAX_VALUE) {
pred[node.leftDeer - 1 + n][node.leftLions - 1 + n] = node;
dist[node.leftDeer - 1 + n][node.leftLions - 1 + n] = dist[node.leftDeer][node.leftLions] + 1;
q.add(new Node(node.leftDeer - 1, node.leftLions - 1, node.rightDeer + 1, node.rightLions + 1, true));
}
}
if (node.leftDeer != 0) {
if (node.rightDeer + 1 == n && node.rightLions == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer][node.leftLions] + 1;
goal = new Node(node.leftDeer - 1, node.leftLions, node.rightDeer + 1, node.rightLions, true);
return;
}
if (dist[node.leftDeer - 1 + n][node.leftLions + n] == Integer.MAX_VALUE) {
pred[node.leftDeer - 1 + n][node.leftLions + n] = node;
dist[node.leftDeer - 1 + n][node.leftLions + n] = dist[node.leftDeer][node.leftLions] + 1;
q.add(new Node(node.leftDeer - 1, node.leftLions, node.rightDeer + 1, node.rightLions, true));
}
}
if (node.leftLions != 0) {
if (node.rightDeer == n && node.rightLions + 1 == n) {
pred[n * 2 + 1][n * 2 + 1] = node;
dist[n * 2 + 1][n * 2 + 1] = dist[node.leftDeer][node.leftLions] + 1;
goal = new Node(node.leftDeer, node.leftLions - 1, node.rightDeer, node.rightLions + 1, true);
return;
}
if (dist[node.leftDeer + n][node.leftLions - 1 + n] == Integer.MAX_VALUE) {
pred[node.leftDeer + n][node.leftLions - 1 + n] = node;
dist[node.leftDeer + n][node.leftLions - 1 + n] = dist[node.leftDeer][node.leftLions] + 1;
q.add(new Node(node.leftDeer, node.leftLions - 1, node.rightDeer, node.rightLions + 1, true));
}
}
}
}
public static void printPath(Node node) {
if (node.leftDeer == -1)
return;
if (node == goal)
printPath(pred[2 * n + 1][2 * n + 1]);
else if (node.isRightBoat)
printPath(pred[node.leftDeer + n][node.leftLions + n]);
else
printPath(pred[node.leftDeer][node.leftLions]);
for (int i = 0; i < node.leftDeer; i++) {
if (i == node.leftDeer - 1)
System.out.print("d ");
else
System.out.print("d");
}
if (node.leftDeer == 0)
System.out.print(" ");
for (int j = 0; j < node.leftLions; j++) {
if (j == node.leftLions - 1)
System.out.print("l ");
else
System.out.print("l");
}
if (node.leftLions == 0)
System.out.print(" ");
System.out.print("| ");
for (int k = 0; k < node.rightDeer; k++) {
if (k == node.rightDeer - 1)
System.out.print("d ");
else
System.out.print("d");
}
if (node.rightDeer == 0)
System.out.print(" ");
for (int l = 0; l < node.rightLions; l++) {
if (l == node.rightLions - 1)
System.out.print("l ");
else
System.out.print("l");
}
System.out.println();
}
}