bzoj4518: [Sdoi2016]征途

赤果果斜率dp…

#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<queue>#include<iostream>#define rep(i,k,n) for(int i=k;i<=(n);i++)#define rep2(i,k,n) for(int i=k;i>=(n);i--)#define mod 1000000007using namespace std;typedef long long ll;const int N=3005;ll d[N],d2[N],sum=0,len[N],sta[N],fr,tail;ll D[105][105];int n,m;inline ll get_y(int a){    return d[a]+len[a]*len[a];}inline ll get_x(int a){return len[a];}int main(){//freopen("journey.in","r",stdin);//freopen("journey.out","w",stdout);ll x;scanf("%d%d",&n,&m);rep(i,1,n){cin>>x;len[i]=len[i-1]+x;sum+=x;}tail=0;if(n<=100){    memset(D,0x7f,sizeof(D));D[0][0]=0;    rep(i,1,m)    rep(j,0,n){        rep(k,0,j){            D[i][j]=min(D[i][j],D[i-1][k]+(len[j]-len[k])*(len[j]-len[k]));        }    }    cout<<m*D[m][n]-sum*sum;    return 0;}    rep(t,1,m){fr=0;        rep(i,1,n){            while(fr<tail && sta[fr]<=i && 2*len[i]*(get_x(sta[fr+1])-get_x(sta[fr]))>(get_y(sta[fr+1])-get_y(sta[fr])))            fr++;            d2[i]=d[sta[fr]]+(len[i]-len[sta[fr]])*(len[i]-len[sta[fr]]);        }        rep(i,1,n)d[i]=d2[i];        tail=0;        rep(i,1,n){            while(tail && (get_y(i)-get_y(sta[tail]))*(get_x(sta[tail])-get_x(sta[tail-1]))< (get_y(sta[tail])-get_y(sta[tail-1]))*(get_x(i)-get_x(sta[tail])))            tail--;            sta[++tail]=i;        }    }    cout<<m*d[n]-sum*sum;    return 0;}