BZOJ 3427 Bytecomputer

易知最后的序列只可能是-1...0....1...

那么直接dp就好。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 1000050
#define inf 1000000007
using namespace std;
int n,x[maxn],dp[maxn][4];
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++) scanf("%d",&x[i]);
    dp[1][0]=dp[1][1]=dp[1][2]=inf;
    dp[1][x[1]+1]=0;
    for (int i=2;i<=n;i++)
    {
        dp[i][0]=dp[i-1][0]+x[i]+1;
        dp[i][1]=(x[i]!=0)*inf+dp[i-1][1];
        if (x[i]==0) dp[i][1]=min(dp[i-1][0],dp[i][1]);
        else if (x[i]==1) dp[i][1]=min(dp[i-1][0]+1,dp[i][1]);
        dp[i][2]=inf;
        if (x[i]==-1) dp[i][2]=min(dp[i][2],dp[i-1][2]+2);
        else if (x[i]==0) dp[i][2]=min(dp[i][2],dp[i-1][2]+1);
        else dp[i][2]=min(dp[i][2],min(dp[i-1][0],min(dp[i-1][1],dp[i-1][2])));
        dp[i][0]=min(dp[i][0],inf);dp[i][1]=min(dp[i][1],inf);dp[i][2]=min(dp[i][2],inf);
    }
    int ret=min(dp[n][0],min(dp[n][1],dp[n][2]));
    if (ret>=inf) printf("BRAK\n");else printf("%d\n",ret);
    return 0;
}