UVA 10253 - Series-Parallel Networks（数论+计数问题+递推）

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <algorithm>
using namespace std;

long long C(long long n, long long m) {
    double ans = 1;
    for (int i = 0; i < m; i++) {
        ans *= n - i;
    }
    for (int i = 0; i < m; i++)
    	ans /= i + 1;
    return (long long)(ans + 0.5);
}

const int N = 31;
int n;
long long f[N];
long long dp[N][N];

int main() {
	f[1] = 1;
    for (int i = 0; i < N; i++) dp[i][0] = 1;
    for (int i = 1; i < N; i++) {dp[i][1] = 1; dp[0][i] = 0;}
    for (int i = 1; i < N; i++) {
        for (int j = 2; j < N; j++) {
            dp[i][j] = 0;
            for (int p = 0; p * i <= j; p++) {
            	dp[i][j] += C(f[i] + p - 1, p) * dp[i - 1][j - p * i];
            }
        }
        f[i + 1] = dp[i][i + 1];
    }
    while (~scanf("%d", &n) && n) {
    	printf("%lld\n", n == 1 ? 1 : 2 * f[n]);
    }
    system("pause");
    return 0;
}