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Solution.java
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Solution.java
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package hackrank.algorithm.graph.snake;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.Scanner;
/**
* @see <a href="https://www.hackerrank.com/challenges/the-quickest-way-up">Snakes and Ladders: The Quickest Way Up</a>
*/
public class Solution {
public static void main(String[] args) {
for (Board board : readInput(System.in)) {
System.out.println(board.quickestWayUp(1, 100));
}
}
private static List<Board> readInput(InputStream input) {
Scanner scanner = new Scanner(input);
int testCases = scanner.nextInt();
List<Board> boards = new ArrayList<>(testCases);
for (int i = 0; i < testCases; i++) {
int numberLadders = scanner.nextInt();
Map<Integer, Integer> ladders = new HashMap<>(numberLadders, 1.0f);
for (int l = 0; l < numberLadders; l++) {
ladders.put(scanner.nextInt(), scanner.nextInt());
}
int numberSnakes = scanner.nextInt();
Map<Integer, Integer> snakes = new HashMap<>(numberSnakes, 1.0f);
for (int s = 0; s < numberSnakes; s++) {
snakes.put(scanner.nextInt(), scanner.nextInt());
}
boards.add(new Board(100, ladders, snakes));
}
scanner.close();
return boards;
}
static class Board {
public Map<Integer, Square> squares;
public Map<Integer, Integer> ladders;
public Map<Integer, Integer> snakes;
public Board(int numberSquares, Map<Integer, Integer> ladders, Map<Integer, Integer> snakes) {
this.squares = new HashMap<>(numberSquares, 1.0f);
this.ladders = ladders;
this.snakes = snakes;
initialize(numberSquares);
}
private void initialize(int numberSquares) {
for (int squareId = 1; squareId <= numberSquares; squareId++) {
add(squareId);
}
for (int squareId = 1; squareId < numberSquares; squareId++) {
connect(squareId, findNextSquares(squareId));
}
}
public List<Integer> findNextSquares(int startId) {
List<Integer> next = new ArrayList<>();
int max = startId + 6;
max = Math.min(max, squares.size());
for (int id = startId + 1; id <= max; id++) {
if (ladders.containsKey(id)) {
next.add(ladders.get(id));
} else if (snakes.containsKey(id)) {
next.add(snakes.get(id));
} else {
next.add(id);
}
}
return next;
}
public void add(int squareId) {
squares.put(squareId, new Square(squareId));
}
public void connect(int idFrom, int idTo) {
Square from = squares.get(idFrom);
Square to = squares.get(idTo);
from.connect(to, 1);
}
public void connect(int idFrom, List<Integer> idsTo) {
for (int idTo : idsTo) {
connect(idFrom, idTo);
}
}
private void computePaths(Square squareStart) {
squareStart.minDistance = 0;
PriorityQueue<Square> vertexQueue = new PriorityQueue<Square>();
vertexQueue.add(squareStart);
while (!vertexQueue.isEmpty()) {
Square squareFrom = vertexQueue.poll();
for (Connection connection : squareFrom.connections) {
Square nodeTo = connection.target;
int distanceTo = squareFrom.minDistance + connection.weight;
if (distanceTo < nodeTo.minDistance) {
vertexQueue.remove(nodeTo);
nodeTo.minDistance = distanceTo;
nodeTo.previous = squareFrom;
vertexQueue.add(nodeTo);
}
}
}
}
public List<Square> findPathTo(int startId, int endId) {
Square start = squares.get(startId);
computePaths(start);
List<Square> path = new ArrayList<Square>();
Square end = squares.get(endId);
if (end.previous != null) {
for (Square square = end; square != null; square = square.previous) {
path.add(square);
}
}
Collections.reverse(path);
return path;
}
/**
* @return Least number of dice rolls for quickest way up from {@code startId} to {@code endId}
*/
public int quickestWayUp(int startId, int endId) {
return findPathTo(startId, endId).size() - 1;
}
}
static class Square implements Comparable<Square> {
public int id;
public List<Connection> connections;
public int minDistance = Integer.MAX_VALUE;
public Square previous;
public Square(int id) {
this.id = id;
this.connections = new ArrayList<>();
}
public void connect(Square square, int weight) {
connections.add(new Connection(square, weight));
}
@Override
public String toString() {
return String.valueOf(id);
}
@Override
public int compareTo(Square other) {
return Integer.compare(minDistance, other.minDistance);
}
}
static class Connection {
public Square target;
public int weight;
public Connection(Square target, int weight) {
this.target = target;
this.weight = weight;
}
}
}