【poj3349】Snowflake Snow Snowflakes（哈希表）

                                                                                               Snowflake Snow Snowflakes

Time Limit: 4000MS

 Memory Limit: 65536KTotal Submissions: 44120 Accepted: 11549

Description

You may have heard that no two snowflakes are alike. Your task is to write a program to determine whether this is really true. Your program will read information about a collection of snowflakes, and search for a pair that may be identical. Each snowflake has six arms. For each snowflake, your program will be provided with a measurement of the length of each of the six arms. Any pair of snowflakes which have the same lengths of corresponding arms should be flagged by your program as possibly identical.

Input

The first line of input will contain a single integer n, 0 < n ≤ 100000, the number of snowflakes to follow. This will be followed byn lines, each describing a snowflake. Each snowflake will be described by a line containing six integers (each integer is at least 0 and less than 10000000), the lengths of the arms of the snow ake. The lengths of the arms will be given in order around the snowflake (either clockwise or counterclockwise), but they may begin with any of the six arms. For example, the same snowflake could be described as 1 2 3 4 5 6 or 4 3 2 1 6 5.

Output

If all of the snowflakes are distinct, your program should print the message:
No two snowflakes are alike.
If there is a pair of possibly identical snow akes, your program should print the message:
Twin snowflakes found.

Sample Input

21 2 3 4 5 64 3 2 1 6 5

    之前学ac自动机等东西的时候，经常看到哈希这个东西，但是一直没有找到博客学。因为之前一直以为hash值是一个特定的计算方法，我还奇怪呢为什么网上找不到一个介绍具体计算方法的，为什么他们都会QAQ

    然后听了朱菊苣的话仔细看了这道最基础的hash题，突然发现，hash好像只是指一种用特性键值建立对应关系的思想，并不是特定的方法，具体hash值随便怎么算，不知道理解的对不对=-=害怕ing。。。

    这道题就是判断输入的雪花里有没有重复的，因为雪花是个圈，所以在比较时考虑每一个角作为起点，并考虑正反方向，全部要比一遍。hash值的计算这里用的就是把六个角的值加起来。

    额，在写着一题的时候，写完后忘记保存然后打开一看变成了helloworld，作为一个懒癌患者实在不想again一遍，所以这个代码基本copy的我看的那篇博客，，，对不起，我有罪。。。。

#include <cstdio>#include <cstring>#include <algorithm>#include <iostream>using namespace std;typedef long long LL;const int maxn=1200010;const int mod=1200007;int head[maxn],p;void init(){    memset(head,-1,sizeof(head));    p=0;}struct note{    int num[6];    int next;} edge[1200010];int get_hash(int *num){    int h=0;    for(int i=0; i<6; i++)        h+=num[i];    return h%mod;}void insert_hash(int *num,int h){    for(int i=0; i<6; i++)        edge[p].num[i]=num[i];    edge[p].next=head[h];    head[h]=p;    p++;}bool compare(int *a,int *b){    for(int i=0; i<6; i++)    {        if(a[i]!=b[i])            return false;    }    return true;}bool search_hash(int *num){    int h=get_hash(num);    for(int i=head[h]; i!=-1; i=edge[i].next)    {        if(compare(num,edge[i].num))            return true;    }    insert_hash(num,h);    return false;}int main(){    int n,num[2][15];    scanf("%d",&n);    init();    int flag=0;    while(n--)    {        for(int i=0; i<6; i++)        {            scanf("%d",&num[0][i]);            num[0][i+6]=num[0][i];        }        if(flag) continue;        for(int i=0; i<6; i++)        {            num[1][i+6]=num[1][i]=num[0][5-i];        }        for(int i=0; i<6; i++)        {            if(search_hash(num[0]+i)||search_hash(num[1]+i))            {                flag=1;                break;            }        }    }    if(flag)printf("Twin snowflakes found.\n");    else printf("No two snowflakes are alike.\n");    return 0;}