LightOJ 1064 - Throwing Dice （dp）

题意:

给定n<25个骰子,求总和至少为x<=150的概率,分数输出

分析:

直接算概率比较麻烦,应该是我不会−−,然后直接求方法数就好了

考虑dp[i][j]:=i个骰子和为j的方法数

ans=∑i>=xdp[n][i]∑dp[n][i]

代码:

//
//  Created by TaoSama on 2015-11-26
//  Copyright (c) 2015 TaoSama. All rights reserved.
//
//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <algorithm>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <string>
#include <set>
#include <vector>

using namespace std;
#define pr(x) cout << #x << " = " << x << "  "
#define prln(x) cout << #x << " = " << x << endl
const int N = 1e5 + 10, INF = 0x3f3f3f3f, MOD = 1e9 + 7;

typedef long long LL;

int n, x;
LL dp[30][200];

void init() {
for(int i = 1; i <= 6; ++i) dp[1][i] = 1;
for(int i = 2; i <= 25; ++i)
for(int j = i; j <= 6 * i; ++j)
for(int k = 1; k <= 6; ++k)
if(j >= k) dp[i][j] += dp[i - 1][j - k];
}

int main() {
#ifdef LOCAL
freopen("C:\\Users\\TaoSama\\Desktop\\in.txt", "r", stdin);
//  freopen("C:\\Users\\TaoSama\\Desktop\\out.txt","w",stdout);
#endif
ios_base::sync_with_stdio(0);

int t; scanf("%d", &t);
int kase = 0;
init();
while(t--) {
scanf("%d%d", &n, &x);
LL up = 0, down = 0;
for(int i = n; i <= 6 * n; ++i) {
if(i >= x) up += dp
[i];
down += dp
[i];
}
LL gcd = __gcd(up, down);
up /= gcd; down /= gcd;
printf("Case %d: ", ++kase);
if(!up) puts("0");
else if(up == down) puts("1");
else printf("%lld/%lld\n", up, down);
}
return 0;
}