hdu 4405概率dp

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

const int maxe = 50000;
const int maxn = 100500;
const int INF  = 0x3f3f3f;

double dp[maxn];
int map[maxn];

int main()
{
    //freopen("E:\\acm\\input.txt","r",stdin);
    int N,M;
    while(cin>>N>>M && N+M){
        for(int i=N;i<=N+5;i++) dp[i] = 0;
        memset(map,0,sizeof(map));
        for(int i=1;i<=M;i++){
            int x,y;
            scanf("%d %d",&x,&y);
            map[x] = y;
        }
        for(int i=N-1;i>=0;i--){
            if(map[i]){
                dp[i] = dp[map[i]];
                continue;
            }
            int a[7];
            double sum = 0;
            for(int j=1;j<=6;j++){
                a[j] = i+j;
                while(map[a[j]]){
                    a[j] = map[a[j]];
                }
                sum += dp[a[j]] + 1;
            }
            dp[i] = sum/6;
        }
        printf("%.4lf\n",dp[0]);
    }
}