学步园

大意略。

见训练指南P198

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>
using namespace std;

const int maxn = 100010;
const int maxd = 20;

int n, m;
int d[maxn][maxd];
int a[maxn];
int num[maxn], lef[maxn], rig[maxn];

vector<int> Count;

int RMQ(int L, int R)
{
	int k = 0;
	while((1<<(k+1)) <= R-L+1) k++;
	return max(d[L][k], d[R-(1<<k)+1][k]);
}

void RMQ_init(const vector<int> &A)
{
	int n = A.size();
	for(int i = 0; i < n; i++) d[i][0] = A[i];
	for(int j = 1; (1<<j) <= n; j++)
	{
		for(int i = 0; i+(1<<j)-1 < n; i++)
		{
			d[i][j] = max(d[i][j-1], d[i+(1<<(j-1))][j-1]);
		}
	}
}

int read_case()
{
	scanf("%d", &n);
	if(!n) return 0;
	scanf("%d", &m);
	for(int i = 0; i < n; i++) scanf("%d", &a[i]);
	a[n] = a[n-1]+1;
	int start = -1;
	for(int i = 0; i <= n; i++)
	{
		if(i == 0 || a[i] > a[i-1])
		{
			if(i > 0)
			{
				Count.push_back(i-start);
				for(int j = start; j < i; j++)
				{
					num[j] = Count.size()-1; lef[j] = start, rig[j] = i-1;
				}
			}
			start = i;
		}
	}
	RMQ_init(Count);
	return 1;
}

void solve()
{
	int ans;
	while(m--)
	{
		int L, R;
		scanf("%d%d", &L, &R); L--, R--;
		if(num[L] == num[R]) ans = R-L+1;
		else
		{
			ans = max(rig[L]-L+1, R-lef[R]+1);
			if(num[L]+1 <= num[R]-1) ans = max(ans, RMQ(num[L]+1, num[R]-1));
		}
		printf("%d\n", ans);
	}
}

int main()
{
	while(read_case())
	{
		solve();
	}
	return 0;
}