hdu4405[Aeroplane chess] 有点懂了期望概率DP

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 1e5 + 10 ;

int nxt
;
double f
;

int main () {
int n , m ;
while ( scanf ( "%d%d" , & n , & m ) != EOF && ( n != 0 || m != 0 ) ) {
memset ( f , 0 , sizeof f ) ;
memset ( nxt , 0 , sizeof nxt ) ;
for ( int i = 1 ; i <= m ; ++ i ) {
int x , y ;
scanf ( "%d%d" , & x , & y ) ;
nxt [x] = y ;
}
for ( int i = n-1 ; i >= 0 ; -- i ){
if ( nxt [i] ) { f [i] = f [ nxt [i] ] ; continue ; }
for ( int j = 6 ; j >= 1 ; -- j )
f [i] += ( f [i+j] ) * ( 1.0 / 6 )  ;
f [i] += 1 ;
}
printf ( "%.4lf\n" , f [0] ) ;
}
return 0 ;
}