LintCode "Post Office Problem" !!!

* Non-intuitive state design

class Solution
{
public:
    /**
     * @param A an integer array
     * @param k an integer
     * @return an integer
     */
    int postOffice(vector<int>& A, int k)
    {
        int n = A.size();
        sort(A.begin(), A.end());

    // Cost btw. 2 houses i-j with 1 post-office - built in the mid
    vector<vector<int>> w(n + , vector<int>(n + ));
    for(int i = ; i <= n; i ++)
    {
        w[i][i] = ;
        for(int j = i + ; j <= n; j ++)
        {
        // Check both odd\even. It holds.
        w[i][j] = w[i][j-] + A[j - ] - A[(i + j) /  - ];
        }
    }

    // main DP
    vector<vector<int>> dp(n + , vector<int>(k + ));
    for(int i = ; i <= n; i++)
    {
        dp[i][] = w[][i];
    }
    for(int i = ; i <= k; i ++) // post-offices
    {
        for(int j = n; j > i; j --) // houses. Low j sets high j
        {
        dp[j][i] = INT_MAX;
        for(int x = i - ; x < j; x ++)
        {
            dp[j][i] = min(dp[j][i], dp[x][i-] + w[x + ][j]);
        }
        }
    }

    return dp[n][k];
    }
};

TODO: DP optimized to O(n^2)