POJ 刷题系列：1753. Flip Game

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201712/P1753.txt";

    public static void main(String[] args) throws IOException {
        new Main().run();
    }


    class State{

        boolean[][] board;

        State(boolean[][] board){
            this.board = board;
        }

        int hash() {
            int n = 4;
            int hash = 0;
            int k = 0;
            for (int i = 0; i < n; ++i) {
                for (int j = 0; j < n; ++j) {
                    boolean f = board[i][j];
                    int bit = f == true ? 1 : 0;
                    hash ^= bit << k;
                    k++;
                }
            }
            return hash;
        }

        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < 4; ++i) {
                for (int j = 0; j < 4; ++j) {
                    sb.append((board[i][j] ? 1 : 0) + (j + 1 == 4 ? "\n" : " "));
                }
            }
            return sb.toString();
        }
    }

    void read() {

        int n = 4;

        int START = 0;
        int END   = 65535;

        boolean[][] board = new boolean[n][n];
        for (int i = 0; i < n; ++i) {
            String line = ns();
            for (int j = 0; j < n; ++j) {
                char c = line.charAt(j);
                board[i][j] = c == 'b';
            }
        }

        Queue<State> queue = new ArrayDeque<State>();
        Set<Integer> vis   = new HashSet<Integer>();
        int[][] dir = {{0, 1},{0, -1},{1, 0},{-1, 0},{0, 0}};

        State hello = new State(board);

        queue.offer(hello);
        vis.add(hello.hash());

        int ans  = -1;
        int turn = 0;
        outer: while (!queue.isEmpty() && ans == -1) {
            int size = queue.size();
            for (int i = 0; i < size; ++i) {
                State cur = queue.poll();
                if (cur.hash() == START || cur.hash() == END) {
                    ans = turn;
                    break outer;
                }
                for (int x = 0; x < n; ++x) {
                    for (int y = 0; y < n; ++y) {
                        State nxt = new State(flip(cur.board, x, y, dir));
                        if (!vis.contains(nxt.hash())) {
                            queue.offer(nxt);
                            vis.add(nxt.hash());
                        }
                    }
                }
            }
            turn ++;
        }
        if (ans == -1) out.println("Impossible");
        else out.println(ans);
    }

    boolean[][] flip(boolean[][] board, int x, int y, int[][] dir){
        int n = 4;
        boolean[][] ans = new boolean[n][n];
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < n; ++j) {
                ans[i][j] = board[i][j];
            }
        }

        for (int[] d : dir) {
            int nx = d[0] + x;
            int ny = d[1] + y;
            if (nx >= 0 && nx < n && ny >= 0 && ny < n) {
                ans[nx][ny] = !board[nx][ny];
            }
        }

        return ans;
    }

    FastScanner in;
    PrintWriter out;

    void run() throws IOException {
        boolean oj;
        try {
            oj = ! System.getProperty("user.dir").equals("F:\\oxygen_workspace\\Algorithm");
        } catch (Exception e) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
        }

        InputStream is = oj ? System.in : new FileInputStream(new File(INPUT));
        in = new FastScanner(is);
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        read();
        out.flush();
        if (!oj){
            System.out.println("[" + (System.currentTimeMillis() - s) + "ms]");
        }
    }

    public boolean more(){
        return in.hasNext();
    }

    public int ni(){
        return in.nextInt();
    }

    public long nl(){
        return in.nextLong();
    }

    public double nd(){
        return in.nextDouble();
    }

    public String ns(){
        return in.nextString();
    }

    public char nc(){
        return in.nextChar();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;
        boolean hasNext;

        public FastScanner(InputStream is) throws IOException {
            br = new BufferedReader(new InputStreamReader(is));
            hasNext = true;
        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (Exception e) {
                    hasNext = false;
                    return "##";
                }
            }
            return st.nextToken();
        }

        String next = null;
        public boolean hasNext(){
            next = nextToken();
            return hasNext;
        }

        public int nextInt() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Integer.parseInt(more);
        }

        public long nextLong() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Long.parseLong(more);
        }

        public double nextDouble() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Double.parseDouble(more);
        }

        public String nextString(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more;
        }

        public char nextChar(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more.charAt(0);
        }
    }

    static class D{

        public static void pp(int[][] board, int row, int col) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < row; ++i) {
                for (int j = 0; j < col; ++j) {
                    sb.append(board[i][j] + (j + 1 == col ? "\n" : " "));
                }
            }
            System.out.println(sb.toString());
        }

        public static void pp(char[][] board, int row, int col) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < row; ++i) {
                for (int j = 0; j < col; ++j) {
                    sb.append(board[i][j] + (j + 1 == col ? "\n" : " "));
                }
            }
            System.out.println(sb.toString());
        }
    }

    static class ArrayUtils {

        public static void fill(int[][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                Arrays.fill(f[i], value);
            }
        }

        public static void fill(int[][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }

        public static void fill(int[][][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }
    }

    static class Num{
        public static <K> void inc(Map<K, Integer> mem, K k) {
            if (!mem.containsKey(k)) mem.put(k, 0);
            mem.put(k, mem.get(k) + 1);
        }
    }
}