cf602B Approximating a Constant Range

B. Approximating a Constant Range

time limit per test 2 seconds

memory limit per test 256 megabytes

input standard input

output standard output

When Xellos was doing a practice course in university, he once had to measure the intensity of an effect that slowly approached equilibrium. A good way to determine the equilibrium intensity would be choosing a sufficiently large number of consecutive data points that seems as constant as possible and taking their average. Of course, with the usual sizes of data, it's nothing challenging — but why not make a similar programming contest problem while we're at it?

You're given a sequence of n data points a1, ..., an. There aren't any big jumps between consecutive data points — for each 1 ≤ i < n, it's guaranteed that |ai + 1 - ai| ≤ 1.

A range [l, r] of data points is said to be almost constant if the difference between the largest and the smallest value in that range is at most 1. Formally, let M be the maximum and m the minimum value of ai for l ≤ i ≤ r; the range [l, r] is almost constant if M - m ≤ 1.

Find the length of the longest almost constant range.

Input

The first line of the input contains a single integer n (2 ≤ n ≤ 100 000) — the number of data points.

The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 100 000).

Output

Print a single number — the maximum length of an almost constant range of the given sequence.

Examples

input

5
1 2 3 3 2

output

4

input

11
5 4 5 5 6 7 8 8 8 7 6

output

5

Note

In the first sample, the longest almost constant range is [2, 5]; its length (the number of data points in it) is 4.

In the second sample, there are three almost constant ranges of length 4: [1, 4], [6, 9] and [7, 10]; the only almost constant range of the maximum length 5 is [6, 10].

 

我有点惊讶。。B题就考dp了，虽然是简单的dp

题意是说给一个序列，保证相邻两项差值不超过1，求一个最长子串长度，要求满足子串中最大值减最小值小于2

意思就是串中只能有相邻的两个数字咯

令f[i][1]表示以第i个数开头，只包含a[i]和a[i]+1两种数字的最长子串

令f[i][2]表示以第i个数开头，只包含a[i]和a[i]-1两种数字的最长子串

然后

a[i]==a[i+1] 则 f[i][1]=f[i+1][1] f[i][2]=f[i+1][2]

a[i]==a[i+1]+1 则 f[i][1]=1 f[i][2]=f[i+1][1]+1

a[i]==a[i+1]-1 则  f[i][2]=1 f[i][1]=f[i+1][2]+1

 

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<queue>
#include<deque>
#include<set>
#include<map>
#include<ctime>
#define LL long long
#define inf 0x7ffffff
#define pa pair<int,int>
#define pi 3.1415926535897932384626433832795028841971
using namespace std;
inline LL read()
{
    LL x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
inline void write(LL a)
{
    if (a<0){printf("-");a=-a;}
    if (a>=10)write(a/10);
    putchar(a%10+'0');
}
inline void writeln(LL a){write(a);printf("\n");}
int n,ans;
int a[100010];
int s1[100010];
int s2[100010];
int main()
{
    n=read();
    for (int i=1;i<=n;i++)a[i]=read();
    s1[n]=s2[n]=ans=1;
    for (int i=n-1;i>=1;i--)
    {
        if (a[i]==a[i+1])s1[i]=s1[i+1]+1,s2[i]=s2[i+1]+1;
        if (a[i]>a[i+1])s1[i]=1,s2[i]=s1[i+1]+1;
        if (a[i]<a[i+1])s2[i]=1,s1[i]=s2[i+1]+1;
        ans=max(ans,max(s1[i],s2[i]));
    }
    printf("%d\n",ans);
}