poj3349找相同的雪花（哈希）

題目傳送門

題目大意：給你n個雪花，每一個雪花的六個棱都有各自的長度，若是存在兩片雪花的每條棱長度對應相同，則輸出一句英文，若是不存在就輸出另一句英文，n和長度都比較大。

思路：第一次真正接觸哈希，查了題解，還沒能經過這道題get到哈希的精髓。這道題是把雪花的六個長度加起來取模的值做爲哈希值，而後把擁有相同哈希值的雪花歸爲一類，每一次輸入新的雪花，就先找到它的那一類，而後這一類中進行遍歷，遍歷的方式也就是在一個環裏面暴力，我對這道題用哈希的理解是，利用哈希值進行分類（和並查集有點像），在類中尋找，減小遍歷的次數。

代碼有詳細註釋。

#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<sstream>
#include<cstring>
#include<bitset>
#include<cstdio>
#include<string>
#include<deque>
#include<stack>
#include<cmath>
#include<queue>
#include<set>
#include<map>
#define INF 0x3f3f3f3f
#define CLR(x,y) memset(x,y,sizeof(x))
#define LC(x) (x<<1)
#define RC(x) ((x<<1)+1)
#define MID(x,y) ((x+y)>>1)
using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
const double PI=acos(-1.0);
int fact[10]= {1,1,2,6,24,120,720,5040,40320,362880};
const int mod = 999983;
const int maxn = 100005;
int tot = 0,n,head[mod+5],v[maxn][6],next[maxn];


int gethash(int id) { //獲得哈希值  每位都加起來取餘
	int hashval=0;
	for(int i=0; i<6; i++) {
		hashval=(hashval%mod+v[id][i]%mod)%mod;
	}
	return hashval;
}
void addvhead(int hashval) { //鄰接表
	next[tot]=head[hashval];//head表示  六位數總和爲 hashval的最後一個元素的標號    next[i]表示i的上一個表示是什麼
	head[hashval]=tot++;//更新head   tot就是當前加入的id
}
bool compare(int id,int x) {
	for(int i=0; i<6; i++) { //順時針 比較
		int f=0;
		for(int st=i,j=0; j<6; j++,st= st+1 >= 6 ? 0 : st+1) {
			if(v[id][st]==v[x][j])f++;
			else break;
		}
		if(f==6)return true;
	}
	for(int i=0; i<6; i++) { //逆時針
		int f=0;
		for(int st=i,j=5; j>=0; j--,st= st+1 >= 6 ? 0 : st+1) {
			if(v[id][st]==v[x][j])f++;
			else break;
		}
		if(f==6)return true;
	}
	return false;
}
bool pd(int id) {
	int hashval=gethash(id);
	for(int i=head[hashval]; i!=-1; i=next[i]) { //遍歷哈希值相同的雪花
		if(compare(id,i))return true;
	}
	addvhead(hashval);

	return false;
}
int main() {
	memset(head,-1,sizeof(head));
	cin>>n;
	bool flag=false;
	for(int i=0; i<n; i++) {
		for(int j=0; j<6; j++)scanf("%d",&v[i][j]);
		if(flag)continue;
		if(pd(i))flag=true;

	}
	if(flag)cout<<"Twin snowflakes found."<<endl;
	else cout<<"No two snowflakes are alike."<<endl;
}

Snowflake Snow Snowflakes

Time Limit: 4000MS		Memory Limit: 65536K
Total Submissions: 47318		Accepted: 12345

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 nlines, 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.