首页 > 代码库 > POJ - 3349 Snowflake Snow Snowflakes (哈希)

POJ - 3349 Snowflake Snow Snowflakes (哈希)

题意:给定n(0 < n ≤ 100000)个雪花,每个雪花有6个花瓣(花瓣具有一定的长度),问是否存在两个相同的雪花。若两个雪花以某个花瓣为起点顺时针或逆时针各花瓣长度依次相同,则认为两花瓣相同。

分析:

1、按雪花各花瓣长度之和对MOD取余哈希。对各雪花,算出哈希值,在哈希表中查询是否有与之相同的花瓣。

2、每个花瓣以某个花瓣为起点顺时针或逆时针共有12种表示方法。

3、注意哈希表中只需保存雪花输入时给定的那组长度值即可。

在哈希表中查询时,再算出该组长度值所对应的12种表示,并一一比较,若将这12种表示提前算好,并存入哈希表,则会超时。

#include<cstdio>#include<cstring>#include<cstdlib>#include<cctype>#include<cmath>#include<iostream>#include<sstream>#include<iterator>#include<algorithm>#include<string>#include<vector>#include<set>#include<map>#include<stack>#include<deque>#include<queue>#include<list>#define lowbit(x) (x & (-x))const double eps = 1e-8;inline int dcmp(double a, double b){    if(fabs(a - b) < eps) return 0;    return a > b ? 1 : -1;}typedef long long LL;typedef unsigned long long ULL;const int INT_INF = 0x3f3f3f3f;const int INT_M_INF = 0x7f7f7f7f;const LL LL_INF = 0x3f3f3f3f3f3f3f3f;const LL LL_M_INF = 0x7f7f7f7f7f7f7f7f;const int dr[] = {0, 0, -1, 1, -1, -1, 1, 1};const int dc[] = {-1, 1, 0, 0, -1, 1, -1, 1};const int MOD = 20000;const double pi = acos(-1.0);const int MAXN = 20000 + 10;const int MAXT = 1e6 + 10;using namespace std;int a[12];struct Node{    int x[6];    void read(){        for(int i = 0; i < 6; ++i) scanf("%d", &x[i]);    }};vector<Node> v[MAXN];int Hash(Node& tmp){    int ans = 0;    for(int i = 0; i < 6; ++i){        (ans += tmp.x[i] % MOD) %= MOD;    }    return ans;}bool judge1(int *q, int *w){    for(int i = 0; i < 6; ++i){        if(q[i] != w[i]) return false;    }    return true;}bool judge(Node& q, Node& w){    int tmp[12];    int t[6];    for(int i = 0; i < 6; ++i) tmp[i] = tmp[i + 6] = q.x[i];    for(int i = 0; i < 6; ++i){        for(int j = i; j < 6 + i; ++j){            t[j - i] = tmp[j];        }        if(judge1(t, w.x)) return true;    }    for(int i = 11; i >= 6; --i){        for(int j = i; j >= i - 5; --j){            t[i - j] = tmp[j];        }        if(judge1(t, w.x)) return true;    }    return false;}int main(){    int n;    scanf("%d", &n);    bool ok = false;    while(n--){        int sum = 0;        Node tmp;        tmp.read();        if(ok) continue;        int id = Hash(tmp);        int len = v[id].size();        v[id].push_back(tmp);        if(len){            for(int i = 0; i < len; ++i){                if(judge(v[id][i], tmp)){                    ok = true;                    break;                }            }        }    }    if(ok){        printf("Twin snowflakes found.\n");    }    else{        printf("No two snowflakes are alike.\n");    }    return 0;}

  

POJ - 3349 Snowflake Snow Snowflakes (哈希)