2016秋季练习

来源：lightOJ1064

很水的DP

代码：

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;typedef long long LL;int n,x;const int MAXN = 200;const int N = 50; LL dp[N][MAXN];LL a[N];inline LL gcd(LL a,LL b) {    if(!b) return a;    else return gcd(b,a%b);}inline void ini(){    a[0] = 1;    a[1] = 6;    for(int i=2;i<N;i++) a[i] = a[i-1]*6;    return ;}inline void DP(){    memset(dp,0,sizeof dp);    for(int i=1;i<=6;i++) dp[1][i] = 1;    for(int i=1;i<=26;i++) {        for(int j=1;j<=i*6;j++){            if(!dp[i][j]) continue;            for(int k=1;k<=6;k++){                dp[i+1][j+k] += dp[i][j];            }        }    }}int main(){    int T,nc = 1;    ini();    DP();    scanf("%d",&T);    while(T--){        scanf("%d%d",&n,&x);        LL sum = 0,ans = 0;        int maxn = n*6;        printf("Case %d: ",nc++);        if(x>maxn) {            puts("0");            continue;        }        for(int i=x;i<=maxn;i++) {            ans += dp[n][i];        }        sum = a[n];        if(sum == ans ){            puts("1");            continue;        }        LL tmp = gcd(ans,sum);        printf("%lld/%lld\n",ans/tmp,sum/tmp);    }    return 0;}