101 to 010 Atcoder CODE FESTIVAL 2017 qual B D

https://www.luogu.org/problemnew/show/AT3575

题解

根本不会。。

错误记录：缺少32行的转移。显然这个转移是必要的

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<vector>
 using namespace std;
 #define fi first
 #define se second
 #define mp make_pair
 #define pb push_back
 typedef long long ll;
 typedef unsigned long long ull;
 typedef pair<int,int> pii;

 int a[],ans[],pre[];
 int n;
 int main()
 {
     int i;
     scanf("%d",&n);
     for(i=;i<=n;++i)
         scanf("%1d",&a[i]);
     for(i=;i<=n;++i)
         pre[i]=a[i]==?i:pre[i-];
     int pre2=;
     for(i=;i<=n;++i)
     {
         if(i>=&&a[i]==&&a[i-]==&&a[i-]==)    pre2=i;
         ans[i]=ans[i-];
         if(i>=&&a[i-]==&&a[i-]==&&a[i]==)
         {
             ans[i]=max(ans[i],ans[pre[i-]]+(i--pre[i-]));
             ans[i]=max(ans[i],ans[pre[i-]+]+(i--(pre[i-]+)));
         }
         if(pre2>pre[i])
         {
             ans[i]=max(ans[i],ans[pre2-]+(i-pre2+));
         }
         //printf("1t%d %d\n",i,ans[i]);
     }
     printf("%d",ans[n]);
     return ;
 }