【HDU】4405 Aeroplane chess

#include <cstdio>
#include <cstring>
using namespace std;
double d[100010];
int n, m, mp[100010], X[1005], Y[1005];
int main() {
	while(scanf("%d%d", &n, &m), !(n==0&&m==0)) {
		for(int i=0; i<m; ++i) scanf("%d%d", &X[i], &Y[i]);
		for(int i=0; i<m; ++i) mp[X[i]]=Y[i];
		for(int i=n-1; i>=0; --i) {
			if(mp[i]) d[i]=d[mp[i]];
			else {
				d[i]=(d[i+1]+d[i+2]+d[i+3]+d[i+4]+d[i+5]+d[i+6])/6+1;
			}
		}
		printf("%.4f\n", d[0]);
		memset(d, 0, sizeof(double)*(n));
		for(int i=0; i<m; ++i) mp[X[i]]=0;
	}
	return 0;
}