poj3666 Making the Grade

思路：

离散化+dp。

实现：

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

const int INF = 0x3f3f3f3f;

int a[2005], b[2005], dp[2005][2005], n;

int solve()
{
    for (int i = n - 1; i >= 0; i--)
    {
        dp[i][n - 1] = min(INF, dp[i + 1][n - 1]) + abs(a[i] - b[n - 1]);
        for (int j = n - 2; j >= 0; j--)
        {
            dp[i][j] = min(INF, dp[i][j + 1] - abs(a[i] - b[j + 1]));
            dp[i][j] = min(dp[i][j], dp[i + 1][j]);
            dp[i][j] += abs(a[i] - b[j]);
        }
    }
    int minn = INF;
    for (int i = 0; i < n; i++)
    {
        minn = min(minn, dp[0][i]);
    }
    return minn;
}
int main()
{
    cin >> n;
    for (int i = 0; i < n; i++)
    {
        scanf("%d", &a[i]);
        b[i] = a[i];
    }
    int minn = INF;
    sort(b, b + n);
    minn = solve();
    cout << minn << endl;
    return 0;
}

总结：

1.初步学会了离散化技巧。

2.初步学会了递推优化，对完全背包的理解更深入了。