很好写的状态转移方程。
dp[i][j]=dp[i-1][k];
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<iostream>
using namespace std;
#define maxn 30030
#define INF 9999999
int dp[maxn][3];
int dps[maxn][3];
int a[maxn];
int main()
{
int n,i,j,k;
while(~scanf("%d",&n))
{
for(i=1;i<=n;i++)
{
scanf("%d",&a[i]);
}
for(i=1;i<=n;i++)dp[i][1]=dp[i][2]=dp[i][3]=INF;
for(i=1;i<=n;i++)dps[i][1]=dps[i][2]=dps[i][3]=INF;
int leap=0;
for(i=1;i<=n;i++)
{
for(j=1;j<=3;j++)
{
if(a[i]!=j)leap=1;
else leap=0;
for(k=1;k<=j;k++)
{
dp[i][j]=min(dp[i][j],dp[i-1][k]+leap);
}
}
}
for(i=1;i<=n;i++)
{
for(j=1;j<=3;j++)
{
if(a[i]!=j)leap=1;
else leap=0;
for(k=3;k>=j;k--)
{
dps[i][j]=min(dps[i][j],dps[i-1][k]+leap);
}
}
}
int minn;
minn=INF;
for(i=1;i<=3;i++)minn=min(minn,min(dp[n][i],dps[n][i]));
cout<<minn<<endl;
}
return 0;
}