整数划分问题--DFS

单点时限:1000ms
内存限制:256MB

描述
Given two positive integers N and M, please divide N into several integers A1, A2, …, Ak (k >= 1), so that:
1. 0 < A1 < A2 < … < Ak;
2. A1 + A2 + … + Ak = N;
3. A1, A2, …, Ak are different with each other;
4. The product of them P = A1 * A2 * … * Ak is a multiple of M;
How many different ways can you achieve this goal?
输入
Two integers N and M. 1 <= N <= 100, 1 <= M <= 50.
输出
Output one integer – the number of different ways to achieve this goal, module 1,000,000,007.
样例输入
7 2
样例输出
4
样例提示
There are 4 different ways to achieve this goal for the sample:
A1=1, A2=2, A3=4;
A1=1, A2=6;
A1=2, A2=5;
A1=3, A2=4.

思路就是暴力 , 把所有情况都试一下.

#include <iostream>using namespace std;typedef unsigned long long ull;ull N, M;ull r = 0;const ull MOD = 1000000007;void dfs (ull i, ull s, ull p) {    if (s == N) {        if (p % M == 0) r++;        return;    }    for (ull j = i + 1; j < N - s + 1; j++) {        dfs (j, s + j, p * j);    }}int main () {    cin >> N >> M;    dfs (0, 0, 1);     cout << r % MOD << endl;    return 0;}