[POJ 3349] Snowflake Snow Snowflakes

题目：一朵雪花有6个花瓣，每个花瓣有一个值，当两片雪花六个对应位置的花瓣都一样时，就是Twin Snowflakes。给出一个雪花的集合，要求查找里面是否有Twin Snowflakes。

思路：哈希的入门题目。如果直接数组存储比较会超时。建立一个哈希表，每读入一片雪花，就先排序，再存入哈希表，如果发现表中已经存储了一样的雪花，就判定为存在Twin Snowflakes，如果所有雪花都存入还没有存入相同的则判定为不存在。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main{
	static Node nodes[];
	static final int SIZE = 10000;
	static boolean flag;

	public static void main(String[] args) throws IOException {
		nodes = new Node[SIZE];
		initHead();
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String input = in.readLine();
		StringTokenizer st = new StringTokenizer(input);
		int N =  Integer.parseInt(st.nextToken());
		for(int i = 0; i < N; i++){
			int map[] = new int[6];
			input = in.readLine();
			st = new StringTokenizer(input);
			for(int j = 0; j < 6; j++){
				map[j] = Integer.parseInt(st.nextToken());
			}
			sort(map);
			int key = getKey(map);
			Node newNode = new Node();
			newNode.value = map;
			insert(key, newNode);
			if(flag)
				break;
		}
		if(!flag){
			System.out.println("No two snowflakes are alike.");
		}else{
			System.out.println("Twin snowflakes found.");
		}
		in.close();
	}
	
	static void initHead(){
		for(int i = 0; i < SIZE; i++){
			nodes[i] = new Node();
			nodes[i].next = nodes[i];
			nodes[i].pre = nodes[i];
		}
	}
	
	static void insert(int key, Node newNode){
		Node cur = nodes[key].next;
		while(cur != nodes[key]){
			if(isSame(cur.value, newNode.value)){
				flag = true;
				return;
			}
			cur = cur.next;
		}
		newNode.pre = cur;
		newNode.next = cur.next;
		newNode.next.pre = newNode;
		cur.next = newNode;
	}
	
	static boolean isSame(int a[], int b[]){
		for(int i = 0; i < 6; i++){
			if(a[i] != b[i])
				return false;
		}
		return true;
	}
	
	static void sort(int a[]){
		for(int i =0; i < 6; i++){
			for(int j = i + 1; j < 6; j++){
				if(a[i] > a[j]){
					int temp = a[i];
					a[i] = a[j];
					a[j] = temp;
				}
			}
		}
	}
	
	static int getKey(int value[]){
		int sum = 0;
		for(int i = 0; i < 6; i++)
			sum += value[i];
		return sum % SIZE;
	}

	static class Node{
		Node next;
		Node pre;
		int value[];
	}
}