UVA 10759 Dice Throwing

题意：求扔出色子总数大于等于x的概率，递推求出dp[i][j]代表扔i个色子有总数是j的个数

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;

long long dp[25][160];

void init(){
    memset(dp,0,sizeof(dp));
    dp[0][0] = 1;
    for (int i = 1; i <= 24; ++i)
        for (int j = 0; j <= 150; j++)
            if (dp[i-1][j])
                for (int k = 1; k <= 6; k++)
                    dp[i][j+k] += dp[i-1][j];
}

long long gcd(long long a,long long b){
    return b==0?a:gcd(b,a%b);
}

int main(){
    init();
    int n,x;
    while (scanf("%d%d",&n,&x) != EOF && n+x){
        long long ans = 0;
        for (int i = x; i <= 150; i++)
            ans += dp[n][i];
        long long cur = 1;
        for (int i = 0; i < n; i++)
            cur *= 6;
        if (ans == 0)
            printf("0\n");
        else {
            long long d = gcd(ans,cur);
            if (ans % cur == 0)
                printf("%lld\n",ans/cur);
            else printf("%lld/%lld\n",ans/d,cur/d);
        }
    }
    return 0;
}