等长水管问题

现有一些水管，想拼接成两根相同长度的水管，求能拼出的最长长度。限制条件如下：水管长度为正整数，单根长度不超过1000，总长不超过1000，水管总根数不超过100.

例：5根水管，长度为1， 2 ， 3 ， 4 ， 6.  由1 + 3 + 4 = 2 + 6， 最长长度为8.

#include <iostream>

using namespace std;


int main()
{
    int n;
    int len[100];
    const int MAXLEN = 501;
    int a[MAXLEN][MAXLEN] = {0};

    cout << "please input the number of waterpipe:";

    cin >> n;

    cout << "please input the length of waterpipes:";
    for (int i = 0; i < n; ++i)     {
        cin >> len[i];
    }

    a[0][0] = 1;

    for (int i = 0; i < n; ++i)

        for (int j = MAXLEN - 1; j >= 0; --j)

            for (int k = MAXLEN - 1; k >= 0; --k)

                if (a[j][k] == 1 || (j - len[i] >= 0 && a[j - len[i]][k] == 1) || (k - len[i] >= 0 && a[j][k - len[i]] == 1))
                    a[j][k] = 1;

    for (int i = MAXLEN - 1; i >= 0; --i)

        if (a[i][i] == 1)  {

            cout << "THe max length is :" << i << endl;

            break;
        }

    return 0;

}