hdu 4576 Robot

http://acm.hdu.edu.cn/showproblem.php?pid=4576
暴力確率DP

#include <cstdio>
#include <vector>
#include <string>
#include <algorithm>
#include <queue>
#include <cstring>
#include <map>
#include <set>
#include <iostream>
#include <cmath>
using namespace std;
#ifdef __GNUC__
#define ll long long
#else
#define ll __int64
#endif

const int MAXN = 205;
double dp[2][MAXN];
int main() 
{
#ifdef __GNUC__
    freopen("in.txt", "r", stdin);
#endif
    int n, m, l, r;
    int k;
    int i;
    while (scanf("%d%d%d%d", &n, &m, &l, &r) != EOF && (n+m+l+r))
    {
        int cur = 0;
        dp[0][0] = 1.0;
        for (i = 1; i < n; ++i)
        {
            dp[0][i] = 0.0;
        }
        while (m--)
        {
            scanf("%d", &k);
            for (int j = 0; j< n; ++j)
            {
                dp[cur^1][j] = 0.5 * dp[cur][(j+k)%n] + 0.5 * dp[cur][(j-k+n)%n];
            }
            cur ^= 1;
        }
        double res = 0.0;
        for (i = l-1; i< r; ++i)
        {
            res += dp[cur][i];     
        }
        printf ("%.4lf
", res);
    }
    return 0;
}