poj3349 Snowflake Snow Snowflakes【HASH】

Snowflake Snow Snowflakes

Time Limit: 4000MS		Memory Limit: 65536K
Total Submissions: 49991		Accepted: 13040

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 by n 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

2
1 2 3 4 5 6
4 3 2 1 6 5

Sample Output

Twin snowflakes found.

Source

CCC 2007

题意：

一朵雪花有六条边，给n朵雪花，问其中有没有相同的雪花。当两个雪花的边都对应相同时，雪花是相同的。

思路：

，其中P是我们选定的一个较大的质数

这个HASH函数把所有的雪花分成了P类，对于每一朵 雪花，定位到head[]这个表头所指向的链表。如果该链表中不包含和这朵雪花相同的雪花，就在表头后插入一个新节点（对于一些题目可以在该节点上记录出现了的次数）。

#include <iostream>
#include <set>
#include <cmath>
#include <stdio.h>
#include <cstring>
#include <algorithm>
#include <map>
using namespace std;
typedef long long LL;
#define inf 0x7f7f7f7f

const int maxn = 1e6 + 5;
int snow[maxn][6], head[maxn], nxt[maxn];
int n, tot, P = 99991;

int H(int *a)
{
    int sum = 0, mul = 1;
    for(int i = 0; i < 6; i++){
        sum = (sum + a[i]) % P;
        mul = (long long)mul * a[i] % P;
    }
    return (sum + mul) % P;
}

bool eequal(int *a, int *b)
{
    for(int i = 0; i < 6; i++){
        for(int j = 0; j < 6; j++){
            bool eq = 1;
            for(int k = 0; k < 6; k++){
                //cout<<a[(i + k) % 6]<<" "<<b[(i + k) % 6]<<endl;
                if(a[(i + k) % 6] != b[(j + k) % 6]) eq = 0;
            }
            if(eq) return 1;
            eq = 1;
            for(int k = 0; k < 6; k++){
                if(a[(i + k) % 6] != b[(j - k + 6) % 6])eq = 0;
            }
            if(eq)return 1;
        }
    }
    return 0;
}

bool insertt(int *a)
{
    int val = H(a);
    //cout<<val<<endl;
    for(int i = head[val]; i; i = nxt[i]){
        //cout<<2<<endl;
        if(eequal(snow[i], a)){
            //cout<<1<<endl;
            return 1;
        }
    }
    ++tot;
    memcpy(snow[tot], a, 6 * sizeof(int));
    nxt[tot] = head[val];
    head[val] = tot;
    return 0;
}

int main()
{
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    scanf("%d", &n);
    //tot = 0;
    //memset(head, 0, sizeof(head));
    for(int i = 1; i <= n; i++){
        int a[10];
        for(int j = 0; j < 6; j++){
            scanf("%d", &a[j]);
        }
        if(insertt(a)){
            printf("Twin snowflakes found.
");
            return 0;
        }
    }
    printf("No two snowflakes are alike.
");


}