[BZOJ2038][2009国家集训队]小Z的袜子(hose)

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <stack>
#include <vector>
#include <queue>
#include <cstring>
#include <string>
#include <map>
#include <set>
using namespace std;

const int BufferSize = 1 << 16;
char buffer[BufferSize], *Head, *Tail;
inline char Getchar() {
    if(Head == Tail) {
        int l = fread(buffer, 1, BufferSize, stdin);
        Tail = (Head = buffer) + l;
    }
    return *Head++;
}
int read() {
    int x = 0, f = 1; char c = Getchar();
    while(!isdigit(c)){ if(c == ‘-‘) f = -1; c = Getchar(); }
    while(isdigit(c)){ x = x * 10 + c - ‘0‘; c = Getchar(); }
    return x * f;
}

#define maxn 50010
#define LL long long
int n, m, col[maxn], has[maxn];
LL Ans[maxn], Bns[maxn];
struct Que { int id, l, r; } qs[maxn], tq[maxn];
bool cmpl(Que a, Que b) { return a.l < b.l; }
bool cmpr(Que a, Que b) { return a.r < b.r; }

LL gcd(LL a, LL b) { return !b ? a : gcd(b, a % b); }

int main() {
	n = read(); m = read();
	for(int i = 1; i <= n; i++) col[i] = read();
	for(int i = 1; i <= m; i++) qs[i].id = i, qs[i].l = read(), qs[i].r = read();
	
	sort(qs + 1, qs + m + 1, cmpl);
//	for(int i = 1; i <= m; i++) printf("%d %d %d\n", qs[i].id, qs[i].l, qs[i].r);
	int mxl = qs[m].l, siz = (int)sqrt(mxl + .5), nl = 1, nr = siz;
	for(int i = 1; i <= m;) {
		int j, k, x;
		for(j = i; j < m && nl <= qs[j].l && qs[j].l <= nr; j++) ;
//		for(x = i; x <= j; x++) printf("here: %d %d %d\n", qs[x].l, qs[x].r, qs[x].id);
		sort(qs + i, qs + j + 1, cmpr);
		i = j + 1; nl = nr + 1; nr = nl + siz - 1;
	}
//	for(int i = 1; i <= m; i++) printf("%d %d %d\n", qs[i].id, qs[i].l, qs[i].r);
	nl = 1, nr = 0; LL ans = 0;
//	has[col[1]] = 1;
	for(int i = 1; i <= m; i++) {
		int ql = qs[i].l, qr = qs[i].r;
		while(qr > nr) nr++, ans += has[col[nr]], has[col[nr]]++;
		while(ql < nl) nl--, ans += has[col[nl]], has[col[nl]]++;
		while(qr < nr) has[col[nr]]--, ans -= has[col[nr]], nr--;
		while(ql > nl) has[col[nl]]--, ans -= has[col[nl]], nl++;
		int len = qr - ql + 1;
		Ans[qs[i].id] = ans; Bns[qs[i].id] = (LL)len * (LL)(len - 1) >> 1ll;
//		printf("%d %d %d %lld %d\n", qs[i].id, ql, qr, ans, len);
	}
	
	for(int i = 1; i <= m; i++) {
		LL a = Ans[i], b = Bns[i], g;
		if(!a){ puts("0/1"); continue; }
		g = gcd(a, b); a /= g; b /= g;
		printf("%lld/%lld\n", a, b);
	}
	
	return 0;
}