链接：
http://www.lydsy.com/JudgeOnline/problem.php?id=2038
题意：
中文题目就不说题意了
题解：
这道题好像是莫队出的。。在bzoj上re了19发之后跑到源题目地址上提交，妥妥的ac
wqnmlgb bzoj
这个oj居然还评测代码风格，93分 哈哈哈
代码：
31 struct node { 32 ll l, r, id; 33 }q[MAXN]; 34 35 ll n, m; 36 ll a[MAXN]; 37 ll pos[MAXN]; 38 pair<ll, ll> ans[MAXN]; 39 ll sum[MAXN]; 40 41 bool cmp(node a, node b) { 42 if (pos[a.l] == pos[b.l]) return a.r < b.r; 43 return a.l < b.l; 44 } 45 46 ll L = 1, R = 0; 47 ll Sum = 0; 48 49 void update(ll x, ll add) { 50 Sum -= sum[a[x]] * (sum[a[x]] - 1) / 2; 51 sum[a[x]] += add; 52 Sum += sum[a[x]] * (sum[a[x]] - 1) / 2; 53 } 54 55 ll gcd(ll a, ll b) { 56 return b == 0 ? a : gcd(b, a%b); 57 } 58 59 int main() { 60 ios::sync_with_stdio(false), cin.tie(0); 61 cin >> n >> m; 62 ll sz = sqrt(n); 63 rep(i, 1, n + 1) { 64 cin >> a[i]; 65 pos[i] = i / sz; 66 } 67 rep(i, 0, m) { 68 cin >> q[i].l >> q[i].r; 69 q[i].id = i; 70 } 71 sort(q, q + m, cmp); 72 rep(i, 0, m) { 73 while (L < q[i].l) update(L++, -1); 74 while (L > q[i].l) update(--L, 1); 75 while (R < q[i].r) update(++R, 1); 76 while (R > q[i].r) update(R--, -1); 77 ll a = Sum, b = (q[i].r - q[i].l + 1)*(q[i].r - q[i].l) / 2; 78 ll t = gcd(a, b); 79 if (a == 0 || b == 0 || t == 0) { 80 ans[q[i].id] = mp(0, 1); 81 continue; 82 } 83 ans[q[i].id].first = a / t; 84 ans[q[i].id].second = b / t; 85 } 86 rep(i, 0, m) cout << ans[i].first << '/' << ans[i].second << endl; 87 return 0; 88 }