POJ 刷题系列:1573. Robot Motion

题意:

一张地图包含N,S,W,E的指令,从指定起点[1, p]出发,是否有一条路径能够走到地图边缘,有则输出路径数,无说明走入了死循环,输出走入循环前和循环的步数。

思路: 用一个时间戳来记录走到当前点的时间点,这样如果走到边缘可直接输出,否则判断该点是否在之前被访问过,拿到该点最先的时间戳,就能求出进入循环前后的步数。

代码如下:

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.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201712/P1573.txt";

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

    int[][] dir = {{0, 1}, {-1, 0}, {0, -1}, {1, 0}}; // E N W S

    void read() {
        while (true) {
            int R = ni();
            int C = ni();
            int P = ni();
            if (R + C + P == 0) break;
            char[][] grid = new char[R][C];
            for (int i = 0; i < R; ++i) {
                String line = ns();
                for (int j = 0; j < C; ++j) {
                    grid[i][j] = line.charAt(j);
                }
            }

            int timeStamp = 0;
            Map<Integer, Integer> map = new HashMap<Integer, Integer>();

            // simulation
            int sr = 0;
            int sc = P - 1;

            while (true) {
                if (sr < 0 || sr >= R || sc < 0 || sc >= C) {
                    out.println(timeStamp + " step(s) to exit");
                    break;
                }

                if (map.containsKey(sr * C + sc)) {
                    out.println(map.get(sr * C + sc) + " step(s) before a loop of " + (timeStamp - map.get(sr * C + sc)) + " step(s)");
                    break;
                }

                map.put(sr * C + sc, timeStamp++);

                if (grid[sr][sc] == 'E') {
                    sr = sr + dir[0][0];
                    sc = sc + dir[0][1];
                }
                else if (grid[sr][sc] == 'N') {
                    sr = sr + dir[1][0];
                    sc = sc + dir[1][1];            
                }
                else if (grid[sr][sc] == 'W') {
                    sr = sr + dir[2][0];
                    sc = sc + dir[2][1];
                }
                else {
                    sr = sr + dir[3][0];
                    sc = sc + dir[3][1];
                }
            }

        }
    }

    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);
        }
    }
}

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