HDU4405 水概率

#include <stdio.h>#include <string.h>#include <algorithm>#include<iostream>#include <cstring>double dp[500000];int qw[500000];using namespace std;int main(){    int n, m;    while (cin >> n >> m)    {        if (n == 0)break;        memset(dp, 0, sizeof(dp));        memset(qw, 0, sizeof(qw));        int q, w;        for (int a = 1;a <= m;a++)        {            scanf("%d%d", &q, &w);            qw[q] = w;        }        for (int a = n - 1;a >= 0;a--)        {            if (qw[a])dp[a] = dp[qw[a]];            else            {                for (int b = 1;b <= 6;b++)dp[a] += dp[a + b] / 6.0;                dp[a] += 1;            }        }        printf("%.4lf\n", dp[0]);    }    return 0;}