[博弈 杂题] Codeforces 794E Round #414 E. Choosing Carrot

这个题 首先我们要知道结论

If n is even, the answer is while if n ≥ 3 is odd, the answer is . (If n = 1 then the answer is obviously a1.)

为什么呢 证明看题解

然后可以动k步就是所有长为n−k子区间的答案的最大值

#include<cstdio>#include<cstdlib>#include<algorithm>using namespace std;inline char nc(){  static char buf[100000],*p1=buf,*p2=buf;  return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;}inline void read(int &x){  char c=nc(),b=1;  for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;  for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;}const int N=300005;int n,a[N];int odd[N],even[N];int ans[N];int main(){  freopen("t.in","r",stdin);  freopen("t.out","w",stdout);  read(n);  for (int i=1;i<=n;i++) read(a[i]),ans[1]=max(ans[1],a[i]);  for (int i=1;i<n;i++){    int len=min(n-i,i);    even[len]=max(even[len],max(a[i],a[i+1]));  }  for (int i=2;i<n;i++){    int len=min(n-i,i-1);    odd[len]=max(odd[len],min(a[i],max(a[i-1],a[i+1])));  }  for (int i=n/2;i;i--)    ans[i<<1]=max(ans[(i+1)<<1],even[i]);  for (int i=(n-1)/2;i;i--)    ans[i<<1|1]=max(ans[(i+1)<<1|1],odd[i]);  for (int i=n;i;i--)    printf("%d ",ans[i]);  return 0;}