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bzoj4759 [Usaco2017 Jan]Balanced Photo
传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=4759
【题解】
排序,从大到小插入,树状数组统计。
# include <vector> # 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 = 2e5 + 10, N = 4e5 + 10; const int mod = 1e9+7; # define RG register # define ST static # define lb(x) (x&(-x)) struct BIT { int c[N], n; inline void set(int _n) { memset(c, 0, sizeof c); n = _n; } inline void edt(int x, int d) { for (; x<=n; x+=lb(x)) c[x] += d; } inline int sum(int x) { int ret = 0; for (; x; x-=lb(x)) ret += c[x]; return ret; } inline int sum(int x, int y) { if(x>y) return 0; return sum(y) - sum(x-1); } }T; int n; vector<int> ps; struct pa { int x, pos; pa() {} pa(int x, int pos) : x(x), pos(pos) {} friend bool operator < (pa a, pa b) { return a.x > b.x; } }p[M]; int L[M], R[M]; int main() { cin >> n; T.set(n); for (int i=1; i<=n; ++i) { scanf("%d", &p[i].x); p[i].pos = i; ps.push_back(p[i].x); } sort(ps.begin(), ps.end()); ps.erase(unique(ps.begin(), ps.end()), ps.end()); for (int i=1; i<=n; ++i) p[i].x = lower_bound(ps.begin(), ps.end(), p[i].x) - ps.begin() + 1; sort(p+1, p+n+1); for (int i=1; i<=n; ++i) { int j = i; while(j<n && p[j+1].x == p[i].x) ++j; for (int k=i; k<=j; ++k) { L[k] = T.sum(1, p[k].pos-1); R[k] = T.sum(p[k].pos+1, n); } for (int k=i; k<=j; ++k) T.edt(p[k].pos, 1); i = j; } int ans = 0; for (int i=1; i<=n; ++i) if(max(R[i], L[i]) > 2*min(R[i], L[i])) ++ans; cout << ans << endl; return 0; }
bzoj4759 [Usaco2017 Jan]Balanced Photo
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