bzoj3156

斜率优化。

注意long long的使用，一不小心就没有用。

把a[i]倒过来放，方程就容易推了。

#include<cstdio>#include<cstdlib>#include<cstring>#define LL long longlong long f[1000005];long long a[1000005];int       q[1000005];long long s[1000005]; double Y(int j){ return f[j]-s[j]+j*j+j;}double X(int j){ return (double)j;  }double slop(LL j1,LL j2){ return (f[j2]-f[j1]-s[j2]+s[j1]+j2*j2-j1*j1-j1+j2)/(double)(j2-j1);    }LL mymin(LL u1,LL u2){ if (u1<u2)return u1; return u2; }int main(){ int n; scanf("%d",&n);     for (int i=n;i>=1;i--) scanf("%lld",&a[i]); for (int i=1;i<=n;i++) s[i]=s[i-1]+i; q[1]=1; int l=1,r=1; f[1]=a[1]; long long ans=f[1]+s[n]-s[1]-n+1; for (int i=2;i<=n;i++) {  while(l<r&&slop(q[l],q[l+1])<i)l++;  int j=q[l];   f[i]=f[j]+s[i-1]-s[j]-(LL)(i-j-1)*j+a[i];  ans=mymin(ans,f[i]+s[n]-s[i]-(LL)(n-i)*i);  while(l<r&&slop(q[r],q[r-1])>slop(q[r],i))r--;  q[++r]=i;  } printf("%lld\n",ans);}