HDU 4405（概率dp）

#pragma warning(disable:4996)
#include
#include
#include
#include
#include
#include
#include

using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 100010;
double dp[MAXN];
int Hash[MAXN];


int main()
{
    int N, M;
    while (cin >> N >> M,N||M)
    {
        memset(dp, 0, sizeof(dp));
        memset(Hash, -1, sizeof(Hash));
        dp[N] = 0;
        for (int i = M; i >= 1; i--)
        {
            int a, b;
            cin >> a >> b;
            Hash[a] = b;
        }
        for (int i = N - 1; i >= 0; i--)
        {
            if (Hash[i] == -1)
            {
                for (int k = 1; k <= 6; k++)
                {
                    dp[i] += dp[i+k] * (1.0 / 6.0);
                }
                dp[i] += 1;
            }
            else
            {
                dp[i] = dp[Hash[i]];
            }
        }
        printf("%.4f\n", dp[0]);
    }
    return 0;
}