牛客网-求和

python3.5

    n, m = [int(x) for x in input().split()]
    res = []
    
    def dfs(k, m):
        global res
        if ((k + n) * (n - k + 1) / 2) < m:
            return
        if (m == 0):  # 这部分是输出的内容
            for i in range(len(res)-1):
                print(res[i],end=' ')
            print(res[-1])
    
        for i in range(k, n + 1):
            if i < m - i or i == m:
                res.append(i)
                dfs(i + 1, m - i)
                res.remove(i)  #这句需要多加注意
    dfs(1, m)

c++：

    #include <iostream>
    #include <algorithm>
    using namespace std;
    int dfs(int n,int k,int m,vector<int>& res)
    {
        if((k+n)*(n-k+1)/2<m)
            return 0;
        if(m==0)
        {
            for(int i =0;i<res.size()-1;i++)
            {
                cout << res[i] << " ";
            }
            cout << res[res.size()-1]<<endl;
        }
        for(int i = k;i<=n;i++)
        {
            if(i==m || i<m-i)
            {
                res.push_back(i);
                dfs(n,i+1,m-i,res);
                res.pop_back();
            }
        }
        return 0;
    }
    int main()
    {
        int n,m;
        cin>>n>>m;
        vector<int> res;
        dfs(n,1,m,res);
        return 0;
    }