Title description
Niuniu now has a sequence of n numbers. Niuniu now wants to take a continuous subsequence, and this subsequence must also be satisfied: only one number can be changed at most to make this continuous subsequence a strictly ascending subsequence. Sequence, Niuniu wants to know the longest length of this continuous subsequence.
Enter description:
The input consists of two lines. The first line includes an integer n (1 ≤ n ≤ 10^5), which is the length of the sequence; the
second line has n integers a_i, representing each number in the sequence (1 ≤ a_i ≤ 10^9 ), separated by spaces.
Output description:
Output an integer, indicating the longest length.
Example 1
enter
6
7 2 3 1 5 6
Output
5
Code
#include<bits/stdc++.h>
using namespace std;
const int N=1e5+100;
int l[N],r[N],a[N];//正向连续递增，反向连续递减
int main()
{
int n;
cin>>n;
for(int i=1;i<=n;i++) cin>>a[i];
for(int i=1;i<=n;i++){
//初始都为1
l[i]=1;
r[i]=1;
}
//递推求两种数列
for(int i=2;i<=n;i++){
if(a[i]>a[i-1]){
l[i]=l[i-1]+1;
}
}
for(int i=n-1;i>=1;i--){
if(a[i]<a[i+1]){
r[i]=r[i+1]+1;
}
}
int ans=0;
for(int i=1;i<=n;i++){
ans=max(ans,l[i]);//可能不需要修改就是最长的了
if(a[i+1]-a[i-1]>=2){
//可修改的情况，需要判断前后是否能连在一起
ans=max(ans,l[i-1]+r[i+1]+1);
}
}
cout<<ans<<endl;
/*for(int i=1;i<=n;i++) cout<<l[i]<<" ";
cout<<endl;
for(int i=1;i<=n;i++) cout<<r[i]<<" ";*/
return 0;
}
/*
6
7 2 3 1 5 6
*/
to sum up
Mainly still thinking mode, as long as you think of the method problem, it is easy to solve