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bzoj3781 小B的询问
传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=3781
【题解】
将x^2差分成1+3+5+...+(x+x-1)即可莫队了。顺手3min码出来了(兹磁啊)
复杂度$O(n\sqrt{n})$
# include <math.h> # include <stdio.h> # include <string.h> # include <iostream> # include <algorithm> // # include <bits/stdc++.h> using namespace std; typedef long long ll; typedef long double ld; typedef unsigned long long ull; const int M = 5e4 + 10; const int mod = 1e9+7; int n, m, K, bl[M], t[M], a[M], B; ll cnt, ans[M]; struct pa { int l, r, id; pa() {} pa(int l, int r, int id) : l(l), r(r), id(id) {} friend bool operator < (pa a, pa b) { return bl[a.l] < bl[b.l] || (bl[a.l] == bl[b.l] && bl[a.r] < bl[b.r]); } }q[M]; inline void add(int x) { t[x] ++; cnt += (t[x] + t[x] - 1); } inline void del(int x) { cnt -= (t[x] + t[x] - 1); t[x] --; } int main() { cin >> n >> m >> K; B = sqrt(n); for (int i=1; i<=n; ++i) scanf("%d", a+i); for (int i=1; i<=m; ++i) scanf("%d%d", &q[i].l, &q[i].r), q[i].id = i; for (int i=1; i<=n; ++i) bl[i] = (i-1)/B+1; sort(q+1, q+m+1); int L = 1, R = 0; for (int i=1; i<=m; ++i) { while(R < q[i].r) ++R, add(a[R]); while(R > q[i].r) del(a[R]), --R; while(L < q[i].l) del(a[L]), ++L; while(L > q[i].l) --L, add(a[L]); ans[q[i].id] = cnt; } for (int i=1; i<=m; ++i) printf("%lld\n", ans[i]); return 0; }
bzoj3781 小B的询问
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