bzoj1609 [Usaco2008 Feb]Eating Together麻烦的聚餐（dp）

#include <cstdio>
#include <cstring>
#define N 30005
int n,a
,dp
[4],ans=0;
inline int min(int x,int y){return x<y?x:y;}
int main(){
//  freopen("a.in","r",stdin);
scanf("%d",&n);
for(int i=1;i<=n;++i) scanf("%d",&a[i]);
memset(dp,0,sizeof(dp));
for(int i=1;i<=n;++i){
dp[i][1]=dp[i-1][1]+(a[i]==1?0:1);
dp[i][2]=min(dp[i-1][2],dp[i-1][1])+(a[i]==2?0:1);
dp[i][3]=min(min(dp[i-1][2],dp[i-1][1]),dp[i-1][3])+(a[i]==3?0:1);
}
ans=min(dp
[1],min(dp
[2],dp
[3]));
for(int i=n;i>=1;--i){
dp[i][1]=dp[i+1][1]+(a[i]==1?0:1);
dp[i][2]=min(dp[i+1][2],dp[i+1][1])+(a[i]==2?0:1);
dp[i][3]=min(min(dp[i+1][2],dp[i+1][1]),dp[i+1][3])+(a[i]==3?0:1);
}
ans=min(min(ans,dp[1][1]),min(dp[1][2],dp[1][3]));
printf("%d\n",ans);
return 0;
}