luogu 4401 矿工配餐 多维dp

五维dp，记忆化搜索会MLE超内存，所以用滚动数组，十分经典

五维dp

#include <bits/stdc++.h>

using namespace std;
const int maxn=100010; 
int n,tp[maxn],now[4][4][4][4],last[4][4][4][4];
char s[maxn];
int trans(char c){
    if(c=='M')return 1;
    if(c=='F')return 2;
    if(c=='B')return 3;
    return -1;
}
int judge(int a,int b,int c){
    if(!a && !b) return 1;
    if(!a )return (b!=c)+1;
    if(a==b && b==c)return 1;
    return (a!=b)+(b!=c)+(c!=a);
}
int main(){
    //freopen("77.in","r",stdin);
    //freopen("77.out","w",stdout);
    scanf("%d",&n);
    scanf("%s",s);
    for(int i=1;i<=n;i++)
        tp[i]=trans(s[i-1]);
    for(int i=n;i>=1;i--){
        memset(now,0,sizeof now);
        int p1,p2;
        for(int a1=0;a1<=3;a1++)
        for(int a2=0;a2<=3;a2++)
        for(int b1=0;b1<=3;b1++)
        for(int b2=0;b2<=3;b2++){
            p1=judge(a1,a2,tp[i]),p2=judge(b1,b2,tp[i]);
            now[a1][a2][b1][b2]=max(last[a2][tp[i]][b1][b2]+p1,last[a1][a2][b2][tp[i]]+p2);
        }swap(now,last);
    }
    printf("%d",last[0][0][0][0]);
    return 0;
}

记忆化搜索

#include <iostream>
#include <cstdio>
using namespace std;
const int maxn=100010; 
int n,tp[maxn],f[maxn][4][4][4][4];

int trans(char c){
    if(c=='M')return 1;
    if(c=='F')return 2;
    if(c=='B')return 3;
    return -1;
}
int judge(int a,int b,int c){
    if(!a && !b) return 1;
    if(!a )return (b!=c)+1;
    if(a==b && b==c)return 1;
    return (a!=b)+(b!=c)+(c!=a);
}
int dp(int now,int a1,int a2,int b1,int b2){
    if(now>n) return 0;
    if(f[now][a1][a2][b1][b2]) return f[now][a1][a2][b1][b2];
    f[now][a1][a2][b1][b2]=max( dp(now+1,a2,tp[now],b1,b2)+judge(a1,a2,tp[now]),dp(now+1,a1,a2,b2,tp[now])+judge(b1,b2,tp[now]) );
    return f[now][a1][a2][b1][b2];    
}
char s[maxn];
int main(){
    freopen("77.in","r",stdin);
    freopen("77.out","w",stdout);
    scanf("%d",&n);
    scanf("%s",s);
    for(int i=1;i<=n;i++){
        int t=trans(s[i-1]);
        tp[i]=t;
    }printf("%d\n",dp(1,0,0,0,0));
    return 0;
}

用于复习了