POJ3666：Making the Grade——题解

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cctype>
#include<stack>
using namespace std;
const int N=2001;
typedef long long ll;
inline ll read(){
    ll X=0,w=0;char ch=0;
    while(!isdigit(ch)){w|=ch==‘-‘;ch=getchar();}
    while(isdigit(ch))X=(X<<3)+(X<<1)+(ch^48),ch=getchar();
    return w?-X:X;
}
inline ll abs(ll a){
    if(a<0)a=-a;
    return a;
}
inline ll min(ll a,ll b){
    if(a<b)return a;
    return b;
}
ll a[N],b[N],n;
struct tree{
    int l,r;
    ll dis,val;
}tr[N];
int merge(int x,int y){
    if(x==0||y==0)return x+y;
    if(tr[x].val<tr[y].val)
    swap(x,y);
    tr[x].r=merge(tr[x].r,y);
    if(tr[tr[x].l].dis<tr[tr[x].r].dis)
    swap(tr[x].l,tr[x].r);
    tr[x].dis=tr[tr[x].r].dis+1;
    return x;
}
stack<int>q,l;
ll solve(){
    ll ans=0;
    for(int i=1;i<=n;i++){
    int id=i,ct=1;
    while(!q.empty()&&tr[q.top()].val>tr[id].val){
        id=merge(q.top(),id);
        q.pop();
        if((l.top()+1)/2+(ct+1)/2>(l.top()+ct+1)/2){
        id=merge(tr[id].l,tr[id].r);
        }
        ct+=l.top();
        l.pop();
    }
    l.push(ct);
    q.push(id);
    }
    int i=n+1;
    while(!q.empty()){
    ll k=tr[q.top()].val;
    int len=l.top();
    l.pop();q.pop();
    while(len--){
        i--;
        ans+=abs(tr[i].val-k);
    }
    }
    return ans;
}
int main(){
    n=read();
    tr[0].dis=-1;
    for(int i=1;i<=n;i++){
    a[i]=b[n-i+1]=read();
    }
    for(int i=1;i<=n;i++){
    tr[i].l=tr[i].r=tr[i].dis=0;
    tr[i].val=a[i];
    }
    ll ans=solve();
    for(int i=1;i<=n;i++){
    tr[i].l=tr[i].r=tr[i].dis=0;
    tr[i].val=b[i];
    }
    ans=min(ans,solve());
    printf("%lld\n",ans);
    return 0;
}