E98 线性DP P10741 [SEERC 2020] Fence Job

视频链接：E98 线性DP P10741 [SEERC 2020] Fence Job_哔哩哔哩_bilibili

 

 

 

P10741 [SEERC 2020] Fence Job - 洛谷

// 线性DP O(n^2)
#include <bits/stdc++.h>
using namespace std;

const int N=3005,M=1e9+7;
int n,a[N],f[N][N];

signed main(){
  scanf("%d",&n);
  for(int i=1;i<=n;i++) scanf("%d",&a[i]);
  for(int i=1;i<=n;i++) f[i][0]=1;
  for(int i=1,l,r;i<=n;i++){
    for(l=i;a[l-1]>a[i];l--);
    for(r=i;a[r+1]>a[i];r++);
    for(int j=1;j<=n;j++){
      f[i][j]=f[i-1][j]+f[i][j-1]*(l<=j&&j<=r);
      f[i][j]%=M;
    }
  }
  cout<<f[n][n];
}

 

// 线性DP O(n^2)
#include<bits/stdc++.h>
using namespace std;

const int N=3005,M=1e9+7;
int n,a[N],f[N];

int main(){
  scanf("%d",&n);
  for(int i=1;i<=n;i++)scanf("%d",&a[i]);
  f[0]=1;
  for(int i=1,l,r;i<=n;i++){
    for(l=i;a[l-1]>a[i];l--);
    for(r=i;a[r+1]>a[i];r++);
    for(int j=l;j<=r;j++){
      f[j]+=f[j-1];
      f[j]%=M;
    }
  }
  cout<<f[n];
}

 

AT_agc058_b [AGC058B] Adjacent Chmax - 洛谷

// 线性DP O(n^2)
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

const int mod=998244353;
int n,a[5005],f[5005];

int main(){
  scanf("%d",&n);
  for(int i=1;i<=n;i++)scanf("%d",&a[i]);
  f[0]=1;a[0]=a[n+1]=n+1;
  for(int i=1,l,r;i<=n;i++){
    for(l=i;a[l-1]<a[i];l--);
    for(r=i;a[r+1]<a[i];r++);
    for(int j=l;j<=r;j++)
      f[j]=(f[j]+f[j-1])%mod; 
  }
  cout<<f[n];
}