HDU4405（期望dp）

标准期望套路，很水。读题看好是到n就可以停止了。

const int maxn = 1e5 + 50;
int n, m;
db dp[maxn];
map<int, int> mp;

int main() {
    while (~scanf("%d %d", &n, &m) && n) {
        rep(i, n, n + 5)    dp[i] = 0;
        mp.clear();
        rep(i, 1, m) {
            int a, b;
            read(a), read(b);
            mp[a] = b;
        }

        db sum = 0;
        irep(i, n - 1, 0) {
            if (mp.count(i)) {
                dp[i] = dp[mp[i]];
            } else {
                dp[i] = sum / 6 + 1.0;
            }
            sum += dp[i] - dp[i + 6];
        }

        printf("%.4lf\n", dp[0]);
    }
    return 0;
}