AcWing - 137 - 雪花雪花雪花 = 哈希

https://www.acwing.com/problem/content/139/

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;

int a[20];
ull ha[20];

ull mod = 1e6 + 7;

unordered_map<ull, vector<vector<int> > > m;

bool check(ull key, vector<int> &vec) {
    auto vi = m.find(key);
    if(vi == m.end())
        return false;
    for(auto v : (vi->second)) {
        bool suc = 1;
        for(int i = 0; i < 7; ++i) {
            if(v[i] != vec[i]) {
                suc = 0;
                break;
            }
        }
        if(suc)
            return true;
    }
    return false;
}

int main() {
#ifdef Yinku
    freopen("Yinku.in", "r", stdin);
#endif // Yinku
    srand(time(0));
    for(int i = 0; i < 12; ++i) {
        ha[i] = rand();
        ha[i] = (ha[i] << 16) | rand();
        ha[i] = (ha[i] << 16) | rand();
        ha[i] = (ha[i] << 16) | rand();
    }
    int n;
    scanf("%d", &n);
    vector<ull> vec;
    vector<int> vv(7);
    while(n--) {
        for(int i = 0; i < 6; ++i) {
            scanf("%d", &a[i]);
            a[i + 6] = a[i];
        }
        vec.clear();
        for(int j = 0; j < 6; ++j) {
            ull cur = 0;
            for(int i = 0; i < 6; ++i) {
                cur += (ha[i] + ((a[i + j] << 32) | a[i + j]));
            }
            vec.push_back(cur);
        }
        reverse(a, a + 12);
        for(int j = 0; j < 6; ++j) {
            ull cur = 0;
            for(int i = 0; i < 6; ++i) {
                cur += (ha[i] + ((a[i + j] << 32) | a[i + j]));
            }
            vec.push_back(cur);
        }
        sort(vec.begin(), vec.end());

        ull key = 0;
        for(int j = 0; j < 12; ++j) {
            key = (key << 4) ^ (ha[j]) ^ (vec[j]);
        }

        sort(a, a + 6);

        vv[0] = 0;
        for(int i = 0; i < 6; ++i) {
            vv[i + 1] = a[i];
            vv[0] += a[i];
        }
        if(check(key, vv)) {
            puts("Twin snowflakes found.");
            return 0;
        }

        m[key].push_back(vv);
    }
    puts("No two snowflakes are alike.");

}

原文地址：https://www.cnblogs.com/Inko/p/11729785.html