hdu4405[Aeroplane chess] 有点懂了期望概率DP

f ( i）表示走到ｉ的期望
f ( i ) = f ( i+j ) * ( 1 / 6 )
f ( i ) = nxt [i]

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int N = 1e5 + 10 ;int nxt [N] ;double f [N] ;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 ;}