# 【HDU6184】Counting Stars（三元环计数）

## Description

https://vjudge.net/problem/HDU-6184

## Code

/************************************************ * Au: Hany01 * Date: Jun 25th, 2018 * Prob: HDU6184 * Email: hany01@foxmail.com * Institute: Yali High School ************************************************/

#include<bits/stdc++.h>

using namespace std;

typedef long long LL;
typedef pair<int, int> PII;
#define File(a) freopen(a".in", "r", stdin), freopen(a".out", "w", stdout)
#define rep(i, j) for (register int i = 0, i##_end_ = (j); i < i##_end_; ++ i)
#define For(i, j, k) for (register int i = (j), i##_end_ = (k); i <= i##_end_; ++ i)
#define Fordown(i, j, k) for (register int i = (j), i##_end_ = (k); i >= i##_end_; -- i)
#define Set(a, b) memset(a, b, sizeof(a))
#define Cpy(a, b) memcpy(a, b, sizeof(a))
#define x first
#define y second
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define ALL(a) (a).begin(), (a).end()
#define SZ(a) ((int)(a).size())
#define INF (0x3f3f3f3f)
#define INF1 (2139062143)
#define debug(...) fprintf(stderr, __VA_ARGS__)
#define y1 wozenmezhemecaia

template <typename T> inline bool chkmax(T &a, T b) { return a < b ? a = b, 1 : 0; }
template <typename T> inline bool chkmin(T &a, T b) { return b < a ? a = b, 1 : 0; }

{
register int _, __; register char c_;
for (_ = 0, __ = 1, c_ = getchar(); c_ < '0' || c_ > '9'; c_ = getchar()) if (c_ == '-') __ = -1;
for ( ; c_ >= '0' && c_ <= '9'; c_ = getchar()) _ = (_ << 1) + (_ << 3) + (c_ ^ 48);
return _ * __;
}

const int maxn = 300005, maxm = 600005;

int n, m, e, beg[maxn], v[maxm], nex[maxm], deg[maxn], cnt[maxm], co[maxn], en[maxn], tim;
PII E[maxm];
LL Ans;

inline void add(int uu, int vv) { v[++ e] = vv, nex[e] = beg[uu], beg[uu] = e; }

int main()
{
#ifdef hany01
File("hdu6184");
#endif

while (scanf("%d%d", &n, &m) != EOF) {
Set(beg, 0), Set(deg, 0), e = 0, Set(en, 0), Set(co, 0), Set(cnt, 0), Ans = 0;
For(i, 1, m) {
if (deg[E[i].x] > deg[E[i].y] || (deg[E[i].x] == deg[E[i].y] && E[i].y > E[i].x)) swap(E[i].x, E[i].y);
}
For(i, 1, m) {
int x = E[i].x, y = E[i].y;
++ tim;
for (register int j = beg[x]; j; j = nex[j])
co[v[j]] = tim, en[v[j]] = j;
for (register int j = beg[y]; j; j = nex[j]) if (co[v[j]] == tim)
++ cnt[j], ++ cnt[i], ++ cnt[en[v[j]]];
}
For(i, 1, m) Ans += (LL)(cnt[i] - 1) * cnt[i] / 2;
cout << Ans << endl;
}

return 0;
}
//过眼年华，动人幽意，相逢几番春换。
// -- 王沂孙《法曲献仙音·聚景亭梅次草窗韵》