POJ 刷题系列：1573. Robot Motion

POJ 刷题系列：1573. Robot Motion

传送门：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);
}
}
}