python/TangDou/KaoShi/小蓝突发奇想2.cpp

#include <bits/stdc++.h>

using namespace std;
int n, m;
int cnt;
vector<int> p1, p2;
/**
  测试数据：
  5 1
  答案：
  3
 */
void dfs(int u) {
    //收集答案
    if (u == n + 1) {
        int s1 = 0, s2 = 0;
        for (int i = 0; i < p1.size(); i++)
            s1 += p1[i];
        for (int i = 0; i < p2.size(); i++)
            s2 += p2[i];
        if (s1 - s2 == m)
            cnt++;
        return;
    }
    p1.push_back(u);
    dfs(u + 1);
    p1.pop_back();

    p2.push_back(u);
    dfs(u + 1);
    p2.pop_back();
}
int main() {
    cin >> n >> m;
    dfs(1);
    cout << cnt << endl;
    return 0;
}