Optimizations for Solitaire SPOJ - algorithm

Question

Problem Code: SOLIT
Problem Link: http://www.spoj.com/problems/SOLIT/
I tried solving the SPOJ problem Solitaire. However, I ended up with a TLE (Time Limit Exceeded). My current solution is taking around 2 seconds to execute. I have no idea how to optimize my solution further in order to reduce the time. So, I would be grateful for any help in this regard.
Link to my solution: https://ideone.com/eySI91
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.StringTokenizer;
class Solitaire {
enum Direction {
TOP, RIGHT, DOWN, LEFT;
};
static class Piece {
int row, col;
public Piece(int row, int col) {
this.row = row;
this.col = col;
}
#Override
public boolean equals(Object o)
{
if (!(o instanceof Piece))
return false;
Piece p = (Piece)o;
return (row==p.row && col==p.col);
}
#Override
public int hashCode()
{
return (row*10 + col)%11;
}
}
static class State {
HashSet<Piece> pieces;
public State() {
pieces = new HashSet<>(11);
}
public State(State s) {
pieces = new HashSet<>(11);
for (Piece p: s.pieces)
pieces.add(new Piece(p.row, p.col));
}
#Override
public boolean equals(Object o) {
if (!(o instanceof State))
return false;
State s = (State) o;
if (pieces.size()!=s.pieces.size())
return false;
for (Piece p: pieces)
{
if (!s.pieces.contains(p))
return false;
}
return true;
}
#Override
public int hashCode() {
final int MOD = 1000000007;
long code = 0;
for (Piece p: pieces) {
code = (code + p.hashCode())%MOD;
}
return (int) code;
}
#Override
public String toString()
{
String res = "";
for (Piece p: pieces)
res = res + " (" + p.row + ", " + p.col + ")";
return res;
}
public int getCloseness(State s)
{
int medianRow=0, medianCol=0, sMedianRow=0, sMedianCol=0;
for (Piece p: pieces)
{
medianRow+=p.row;
medianCol+=p.col;
}
medianRow/=4;
medianCol/=4;
for (Piece p: s.pieces)
{
sMedianRow+=p.row;
sMedianCol+=p.col;
}
sMedianRow/=4;
sMedianCol/=4;
int closeness = ((sMedianCol-medianCol)*(sMedianCol-medianCol)) + ((sMedianRow-medianRow)*(sMedianRow-medianRow));
return closeness;
}
}
static State makeMove(State curr, Piece piece, Direction dir, HashSet<State> visited) {
if (dir == Direction.TOP) {
if (piece.row==1)
return null;
if (curr.pieces.contains(new Piece(piece.row-1, piece.col)))
{
if (piece.row==2 || curr.pieces.contains(new Piece(piece.row-2, piece.col)))
return null;
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row-2, piece.col));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row-1, piece.col));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else if (dir == Direction.RIGHT) {
if (piece.col==8)
return null;
if (curr.pieces.contains(new Piece(piece.row, piece.col+1)))
{
if (piece.col==7 || curr.pieces.contains(new Piece(piece.row, piece.col+2)))
return null;
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row, piece.col+2));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row, piece.col+1));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else if (dir == Direction.DOWN) {
if (piece.row==8)
return null;
if (curr.pieces.contains(new Piece(piece.row+1, piece.col)))
{
if (piece.row==7 || curr.pieces.contains(new Piece(piece.row+2, piece.col)))
return null;
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row+2, piece.col));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row+1, piece.col));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else // dir == Direction.LEFT
{
if (piece.col==1)
return null;
if (curr.pieces.contains(new Piece(piece.row, piece.col-1)))
{
if(piece.col==2 || curr.pieces.contains(new Piece(piece.row, piece.col-2)))
return null;
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row, piece.col-2));
if (visited.contains(newState))
return null;
else
return newState;
}
}
else
{
State newState = new State(curr);
newState.pieces.remove(new Piece(piece.row, piece.col));
newState.pieces.add(new Piece(piece.row, piece.col-1));
if (visited.contains(newState))
return null;
else
return newState;
}
}
}
static boolean isReachableInEightMoves(State src, State target) {
Queue<State> q = new LinkedList<>();
HashSet<State> visited = new HashSet<>();
int closeness = src.getCloseness(target);
q.add(src);
int moves = 0;
while (!q.isEmpty() && moves <= 8) {
int levelNodes = q.size();
for (int i = 0; i < levelNodes; i++) {
State curr = q.remove();
if (curr.equals(target))
return true;
if (moves==8)
continue;
visited.add(curr);
for (Piece p: curr.pieces)
{
State newState = makeMove(curr, p, Direction.TOP, visited);
if (newState!=null)
{
int newCloseness = newState.getCloseness(target);
if (closeness>=newCloseness)
{
closeness=newCloseness;
visited.add(newState);
q.add(newState);
}
}
newState = makeMove(curr, p, Direction.RIGHT, visited);
if (newState!=null)
{
int newCloseness = newState.getCloseness(target);
if (closeness>=newCloseness)
{
closeness=newCloseness;
visited.add(newState);
q.add(newState);
}
}
newState = makeMove(curr, p, Direction.DOWN, visited);
if (newState!=null)
{
int newCloseness = newState.getCloseness(target);
if (closeness>=newCloseness)
{
closeness=newCloseness;
visited.add(newState);
q.add(newState);
}
}
newState = makeMove(curr, p, Direction.LEFT, visited);
if (newState!=null)
{
int newCloseness = newState.getCloseness(target);
if (closeness>=newCloseness)
{
closeness=newCloseness;
visited.add(newState);
q.add(newState);
}
}
}
}
moves++;
}
return false;
}
public static void main(String[] args) throws IOException {
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(
new FileOutputStream(FileDescriptor.out), "ASCII"));
CustomScanner sc = new CustomScanner();
int t = sc.nextInt();
long start = System.currentTimeMillis();
while (t-- > 0) {
State src = new State(), target = new State();
for (int i = 0; i < 4; i++) {
src.pieces.add(new Piece(sc.nextInt(), sc.nextInt()));
}
for (int i = 0; i < 4; i++) {
target.pieces.add(new Piece(sc.nextInt(), sc.nextInt()));
}
if (isReachableInEightMoves(src, target))
out.write("YES");
else
out.write("NO");
out.newLine();
}
long end = System.currentTimeMillis();
out.write("Time to execute = " + Double.toString((end-start)/1000d));
out.flush();
}
static class CustomScanner {
BufferedReader br;
StringTokenizer st;
public CustomScanner() {
br = new BufferedReader(new InputStreamReader(System.in));
}
private String next() {
while (st == null || !st.hasMoreElements()) {
try {
st = new StringTokenizer(br.readLine());
} catch (IOException e) {
e.printStackTrace();
}
}
return st.nextToken();
}
public int nextInt() {
return Integer.parseInt(next());
}
public long nextLong() {
return Long.parseLong(next());
}
public double nextDouble() {
return Double.parseDouble(next());
}
public String nextLine() {
String str = "";
try {
str = br.readLine();
} catch (IOException e) {
e.printStackTrace();
}
return str;
}
}
}
Some notes regarding the implementation:-
I am just doing a simple bfs traversal where each node is a state of
the board.
I have defined a function called getCloseness() which measures the closeness of two different states. It is basically the square of the distance between the centroids of the two states. A centroid of a state is the sum of all row values of each piece divided by 4 and the same for columns.
After calculating each state, I am checking if the closeness of this new state is lesser than or equal to the current closeness.
If it is not closer, then I will simply discard the new discovered state.
If it is closer, then I will update the closeness value and insert this new state into the Queue for future processing.
This process terminates when either the queue becomes empty or a state is discovered which is same as the target state.
The above approach takes approximately 1-3 seconds for cases where a minimum of 7 moves are required. I would be grateful if you can tell me how I can further optimize this solution.
The expected time according to the problem is 0.896s.