POJ 刷題系列：3349. Snowflake Snow Snowflakes
傳送門：3349. Snowflake Snow Snowflakes
題意：
每個雪花都有六個分支，用六個整數代表，這六個整數是從任意一個分支開始，朝順時針或逆時針方向遍歷得到的。輸入多個雪花，判斷是否有形狀一致的雪花存在。
思路：
和HASH檢測衝突的原理很像，先對6個數進行HASH而不管順序，這樣只是順序不同，但6個數相同的都會落到同一個鏈表中，但衝突的畢竟是少數，針對衝突的這些數組，判斷雪花是否相等（此處暴力判斷，JAVA水過）。
代碼如下：
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.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;
public class Main{
String INPUT = "./data/judge/201801/P3349.txt";
public static void main(String[] args) throws IOException {
new Main().run();
}
List<Integer>[] set;
int[][] nums;
int mlen = 100007;
void hash(int i, int[] num) {
long sum = 0;
for (int j = 0; j < 6; ++j) {
sum += (long)num[j] * (long)num[j];
sum %= mlen;
}
int key = (int)sum;
set[key].add(i);
}
boolean judge(int i, int j) {
int[] num1 = nums[i];
int[] num2 = nums[j];
StringBuilder sb = new StringBuilder();
for (int x = 0; x < 6; ++x) sb.append(num1[x]);
String cmp = sb.toString();
for (int x = 0; x < 6; ++x) {
int y = x;
int z = x;
StringBuilder lf = new StringBuilder();
StringBuilder rt = new StringBuilder();
do {
lf.append(num2[y]);
rt.append(num2[z]);
y = (y + 1) % 6;
z = (z - 1 + 6) % 6;
}
while(y != x);
if (cmp.equals(lf.toString()) || cmp.equals(rt.toString())) return true;
}
return false;
}
void read() {
int n = ni();
set = new ArrayList[mlen];
for (int i = 0; i < mlen; ++i) set[i] = new ArrayList<Integer>();
nums = new int[n][6];
for (int i = 0; i < n; ++i) {
for (int j = 0; j < 6; ++j) {
nums[i][j] = ni();
}
hash(i, nums[i]);
}
for (int i = 0; i < mlen; ++i) {
if (set[i].size() > 1) {
int len = set[i].size();
for (int x = 0; x < len - 1; ++x) {
for (int y = x + 1; y < len; ++y) {
if (judge(set[i].get(x), set[i].get(y))) {
out.println("Twin snowflakes found.");
return;
}
}
}
}
}
out.println("No two snowflakes are alike.");
}
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);
}
}
}
