ACM 组合数学

//C(n,r)
int c(int n,int r){
    int c=1;
    for(int i=0;i<r;i++) c=c*(n-i)/(i+1);
    return c;
}

//排列生成函数 next_permutation
    string str;
    cin >> str;
    sort(str.begin(), str.end());
    cout << str << endl;
    while(next_permutation(str.begin(), str.end())){
        cout << str << endl;
    }

//母函数模板
const int maxn = 10010;
int c1[maxn], c2[maxn];

int main()
{
    int num;
    int i,j,k;  
    while(~scanf("%d", &num)){
        for(int i = 0; i <= num; i++){
            c1[i] = 1;
            c2[i] = 0;
        }
        for(int i = 2; i <= num; i++){
            for(int j = 0; j <= num; j++){
                for(int k = 0; k+j <= num; k += i){
                    c2[j+k] += c1[j];
                }
            }
            for(int j = 0; j <= num; j++){
                c1[j] = c2[j];
                c2[j] = 0;
            }
        }

    printf("%d\n", c1[num]);
    }

}