单调队列用法整理

双端队列 + pair

pair 类型的变量下可以直接进行比较。

在不同 pair 的比较中，自动把 x.first 当作第一关键字，x.second 当作第二关键字。

1 定义队列

deque <pair <int, int> > q;

2 定义 pair

pair <int, int> nw = make_pair (x, y);

3 前端、后端插入

q.push_back (make_pair (x, y));

q.push_front (make_pair (x, y));

或者：

pair <int, int> nw = make_pair (x, y);
q.push_front (nw);//后端同理

4 前端、后端弹出

q.pop_back ();

q.pop_front ();

5 清空

q.clear ();

6 带有 pair 的访问

x = q.back ().first, id = q.back ().second;

前端同理。

单调队列

P1886 滑动窗口 /【模板】单调队列

代码

#include<bits/stdc++.h>
using namespace std;

#define int long long
#define rint register int
const int maxn = 1e6 + 5;
int n, k;
int a[maxn];

inline int read ()
{
	int x = 1, s = 0;
	char ch = getchar ();
	while (ch < '0' or ch > '9')
	{
		if (ch == '-') x = -1;
		ch = getchar ();
	}
	while (ch >= '0' and ch <= '9') 
		s = s * 10 + ch - '0', ch = getchar ();
	return s * x;
}

deque <pair <int, int> > q;

inline void minn ()
{
	for (rint i (1); i <= n; ++i)
	{
		while (!q.empty () and q.front ().second + k - 1 < i) 
			q.pop_front ();
		while (!q.empty () and q.back ().first > a[i])
			q.pop_back ();
		q.push_back (make_pair (a[i], i));
		if (i >= k) 
        	printf ("%lld ", q.front ().first);
	}
	printf ("\n");
}

inline void maxx ()
{
	q.clear ();
	for (rint i (1); i <= n; ++i)
	{
		while (!q.empty () and q.front ().second + k - 1 < i)
			q.pop_front ();
		while (!q.empty () and q.back ().first < a[i])
			q.pop_back ();
		q.push_back (make_pair (a[i], i));
		if (i >= k) 
        	printf ("%lld ", q.front ().first);
	}
}

signed main ()
{
	n = read (), k = read ();
	for (rint i (1); i <= n; ++i) a[i] = read ();
	minn (), maxx ();
	return 0;
}

当然了，这题指针模拟双端队列也可以的。

——$End$——

CSP2021 RP += INF;