【NOIP2018pj】摆渡车

题面

https://www.luogu.org/problem/P5017

题解

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>

using namespace std;
long long n,m,f[155000],truetime[155000],t[550],nowt[550];
long long sum[155000],cnt[155000];

long long dp(int x){
  if (x<=nowt[1]) return 0; else return f[x];
}

long long count(int l,int r) {
  if (l<nowt[1]) l=0;
  long long s=sum[r]-sum[l],p=cnt[r]-cnt[l];
  s-=p*truetime[l];
  s=p*(truetime[r]-truetime[l])-s;
  return s;
}

int main(){
  int i,j;
  scanf("%lld %lld",&n,&m);
  for (i=1;i<=n;i++) {
    scanf("%lld",&t[i]);
    t[i]+=500;
  }
  sort(t+1,t+n+1);
  t[0]=0;
  for (i=1;i<=n;i++) if (t[i]-t[i-1]>2*m) {
    nowt[i]=nowt[i-1]+2*m;
    truetime[nowt[i]]=t[i];
  }
  else nowt[i]=nowt[i-1]+(t[i]-t[i-1]);
  for (i=1;i<=nowt[n]+500;i++) if (truetime[i]==0) truetime[i]=truetime[i-1]+1;
  for (i=1;i<=n;i++) {
    sum[nowt[i]]+=truetime[nowt[i]];
    cnt[nowt[i]]++;
  }
  for (i=1;i<=nowt[n]+500;i++) sum[i]+=sum[i-1],cnt[i]+=cnt[i-1];
  memset(f,0x3f,sizeof(f));
  f[nowt[1]]=0;
  for (i=1;i<=nowt[n]+500;i++)
    for (j=i-m;j>=i-20*m;j--) if (dp(j)+count(j,i)<f[i]) f[i]=dp(j)+count(j,i);
  long long ans=987654321*987654321LL;
  for (i=nowt[n];i<=nowt[n]+500;i++) if (f[i]<ans) ans=f[i];
  printf("%lld\n",ans);
}