[luoguP1975] [国家集训队]排队（分块）

Posted 2020-10-21 蒟蒻zht的博客

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直接暴力分块，然后在每一个块内排序。

查询时可以在每一个块内二分。

 

#include <cmath>
#include <cstdio>
#include <iostream>
#include <algorithm>
#define M 210
#define N 20101

using namespace std;

int n, m, t, S, C, ans;
int a[N], b[N], c[N], st[M], ed[M], belong[N], sorted[M][M], len[M];

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;
	return x * f;
}

inline int query(int x)
{
	int ret = 0;
	for(; x; x -= x & -x) ret += c[x];
	return ret;
}

inline void add(int x)
{
	for(; x <= m; x += x & -x) c[x]++;
}

inline void init()
{
	int i, j;
	S = sqrt(n);
	for(i = 1; i <= n; i += S)
	{
		st[++C] = i;
		ed[C] = min(i + S - 1, n);
		len[C] = ed[C] - st[C] + 1;
	}
	for(i = 1; i <= C; i++)
	{
		for(j = st[i]; j <= ed[i]; j++)
			belong[j] = i, sorted[i][j - st[i] + 1] = a[j];
		sort(sorted[i] + 1, sorted[i] + len[i] + 1);
	}
}

inline void solve(int x, int y)
{
	if(x > y) swap(x, y);
	int i, l = belong[x], r = belong[y], tmp;
	if(l == r)
		for(i = x + 1; i < y; i++)
		{
			ans -= (a[i] < a[x]);
			ans += (a[i] > a[x]);
			ans -= (a[i] > a[y]);
			ans += (a[i] < a[y]);
		}
	else
	{
		for(i = l + 1; i < r; i++)
		{
			ans -= lower_bound(sorted[i] + 1, sorted[i] + len[i] + 1, a[x]) - sorted[i] - 1;
			ans += len[i] - (upper_bound(sorted[i] + 1, sorted[i] + len[i] + 1, a[x]) - sorted[i]) + 1;
			ans -= len[i] - (upper_bound(sorted[i] + 1, sorted[i] + len[i] + 1, a[y]) - sorted[i]) + 1;
			ans += lower_bound(sorted[i] + 1, sorted[i] + len[i] + 1, a[y]) - sorted[i] - 1;
		}
		for(i = x + 1; i <= ed[l]; i++)
		{
			ans -= (a[i] < a[x]);
			ans += (a[i] > a[x]);
			ans -= (a[i] > a[y]);
			ans += (a[i] < a[y]);
		}
		for(i = st[r]; i < y; i++)
		{
			ans -= (a[i] < a[x]);
			ans += (a[i] > a[x]);
			ans -= (a[i] > a[y]);
			ans += (a[i] < a[y]);
		}
	}
	if(a[x] > a[y]) ans--;
	if(a[x] < a[y]) ans++;
	swap(a[x], a[y]);
	for(i = st[l]; i <= ed[l]; i++) sorted[l][i - st[l] + 1] = a[i];
	for(i = st[r]; i <= ed[r]; i++) sorted[r][i - st[r] + 1] = a[i];
	sort(sorted[l] + 1, sorted[l] + len[l] + 1);
	sort(sorted[r] + 1, sorted[r] + len[r] + 1);
}

int main()
{
	int i, x, y;
	n = read();
	for(i = 1; i <= n; i++) a[i] = b[i] = read();
	sort(b + 1, b + n + 1);
	m = unique(b + 1, b + n + 1) - b - 1;
	for(i = 1; i <= n; i++)
	{
		a[i] = lower_bound(b + 1, b + m + 1, a[i]) - b;
		ans += i - query(a[i]) - 1, add(a[i]);
	}
	printf("%d\n", ans);
	init();
	t = read();
	while(t--)
	{
		x = read();
		y = read();
		solve(x, y);
		printf("%d\n", ans);
	}
	return 0;
}