luogu2893 [USACO08FEB]修路Making the Grade

ref

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
typedef long long ll;
int n, m, a[2005], b[2005];
ll dp[2005][2005];
ll f(){
    memset(dp, 0x3f, sizeof(dp));
    dp[0][1] = 0;
    for(int i=1; i<=n; i++){
        ll val=0x3f3f3f3f3f3f3f3f;
        for(int j=1; j<=m; j++){
            val = min(val, dp[i-1][j]);
            dp[i][j] = val + abs(a[i] - b[j]);
        }
    }
    ll re=0x3f3f3f3f3f3f3f3f;
    for(int i=1; i<=m; i++)
        re = min(re, dp[n][i]);
    return re;
}
int main(){
    cin>>n;
    for(int i=1; i<=n; i++){
        scanf("%d", &a[i]);
        b[i] = a[i];
    }
    sort(b+1, b+1+n);
    m = unique(b+1, b+1+n) - (b + 1);
    ll val=f();
    reverse(a+1, a+1+n);
    val = min(val, f());
    cout<<val<<endl;
    return 0;
}