hdoj：2058

#include <iostream>
#include <cmath>
#include <vector>
using namespace std;

struct node{
    int left;
    int right;
};
int main()
{
    long  N, M;
    long long sum = ;
    vector<node> nodes;
    while (cin >> N >> M)
    {
        if (N ==  && M == )
            break;

        for (long n = N; n >=; n--)
        {
            if ((*M-n*n+n)%(*n)!=)
                continue;
            long long a1 = ( * M - n*n + n) / ( * n);

            long long an = a1 + n - ;
            if (a1 >=  && a1 <= N && an >=  && an <= N && a1 <= an)
            {
                //node node;
                //node.left = a1;
                //node.right = an;
                //nodes.push_back(node);
                cout << "[" << a1 << "," << an << "]" << endl;
            }
        }
        //for (node node : nodes)
        //{
        //    cout << "[" << node.left << "," << node.right << "]" << endl;
        //}
        cout << endl;
    }
    return ;
}

超时

a1 = k

an = k + n - 1

M = n*(2k+n-1)/2

解的

k = M/n - (n-1)/2，这个不能这样写，要写在一起

(2M-n*n-n)/(2*n)。否则对于30/4 - 3/2，会忽略这样的结果，如果先通分当然也就可以。

超时

利用a1>=1这个条件可以减少循环次数

2M - n*n >n

2M > n*n - n>n*n

sqrt(2M)>n

#include <iostream>
#include <cmath>
#include <vector>
using namespace std;

struct node{
    int left;
    int right;
};
int main()
{
    long  N, M;
    long long sum = ;
    vector<node> nodes;
    while (cin >> N >> M)
    {
        if (N ==  && M == )
            break;

        for (long n = sqrt(*M); n >=; n--)
        {
            if ((*M-n*n+n)%(*n)!=)
                continue;
            long a1 = ( * M - n*n + n) / ( * n);

            long an = a1 + n - ;
            if (a1 >=  && a1 <= N && an >=  && an <= N && a1 <= an)
            {
                //node node;
                //node.left = a1;
                //node.right = an;
                //nodes.push_back(node);
                cout << "[" << a1 << "," << an << "]" << endl;
            }
        }
        //for (node node : nodes)
        //{
        //    cout << "[" << node.left << "," << node.right << "]" << endl;
        //}
        cout << endl;
    }
    return ;
}