【DP】 HDOJ 4405 Aeroplane chess

简单DP。。。倒着DP即可。。。

#include <iostream>  
#include <queue>  
#include <stack>  
#include <map>  
#include <set>  
#include <bitset>  
#include <cstdio>  
#include <algorithm>  
#include <cstring>  
#include <climits>  
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 100005
#define maxm 150000
#define eps 1e-10
#define mod 1000000007
#define INF 999999999
#define lowbit(x) (x&(-x))
#define mp mark_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R  
//typedef vector<int>::iterator IT;
typedef long long LL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='\n')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
// head

struct node
{
	int a, b;
}t[maxn];
double dp[maxn];
int n, m;

int cmp(node a, node b)
{
	return a.a > b.a;
}
void read(void)
{
	for(int i = 1; i <= m; i++) scanf("%d%d", &t[i].a, &t[i].b);
}
void work(void)
{
	memset(dp, 0, sizeof dp);
	sort(t+1, t+m+1, cmp);
	for(int i = n-1, j = 1; i >= 0; i--) {
		if(j <= m && t[j].a == i) dp[i] = dp[t[j++].b];
		else for(int k = 1; k <= 6; k++) dp[i] += (dp[i+k] + 1) * 1.0 / 6;
	}
	printf("%.4f\n", dp[0]);
}
int main(void)
{
	while(scanf("%d%d", &n, &m), n | m) {
		read();
		work();
	}
	return 0;
}