Making the Grade POJ - 3666

A straight dirt road connects two fields on FJ's farm, but it changes elevation more than FJ would like. His cows do not mind climbing up or down a single slope, but they are not fond of an alternating succession of hills and valleys. FJ would like to add and remove dirt from the road so that it becomes one monotonic slope (either sloping up or down).

You are given N integers A₁, ... , A_N (1 ≤ N ≤ 2,000) describing the elevation (0 ≤ A_i ≤ 1,000,000,000) at each of N equally-spaced positions along the road, starting at the first field and ending at the other. FJ would like to adjust these elevations to a new sequence B₁, . ... , B_N that is either nonincreasing or nondecreasing. Since it costs the same amount of money to add or remove dirt at any position along the road, the total cost of modifying the road is

| A ₁ - B ₁| + | A ₂ - B ₂| + ... + | A_N - B_N |

Please compute the minimum cost of grading his road so it becomes a continuous slope. FJ happily informs you that signed 32-bit integers can certainly be used to compute the answer.

Input

* Line 1: A single integer: N
* Lines 2..N+1: Line i+1 contains a single integer elevation: A_i

Output

* Line 1: A single integer that is the minimum cost for FJ to grade his dirt road so it becomes nonincreasing or nondecreasing in elevation.

Sample Input

7
1
3
2
4
5
3
9

Sample Output

3

真是傻，5555555555
dp[i][j]表示1~i这段变成非递减数列且末尾是b[j]所需要的最小花费。之所以用b[j],是因为改变过后的数一定会在原来的数列中出现（好厉害），不过我？？？？。

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
using namespace std;
typedef long long ll;

const int maxn=2005;

int n;
int a[maxn],b[maxn];
ll dp[maxn][maxn];

void solve(){
    memset(dp,0,sizeof(dp));
    for(int i=1;i<=n;i++){
        ll temp=dp[i-1][1];
        for(int j=1;j<=n;j++){
            temp=min(temp,dp[i-1][j]);
            dp[i][j]=abs(b[j]-a[i])+temp;
        }
    }
    ll ans=dp[n][1];
    for(int i=2;i<=n;i++) ans=min(ans,dp[n][i]);
    cout<<ans<<endl;
}

int main()
{   cin>>n;
    for(int i=1;i<=n;i++){ cin>>a[i]; b[i]=a[i]; }
    sort(b+1,b+n+1);
    solve();
    
    return 0;
}