[恢]hdu 2062

2011-12-20 16:07:00

地址：http://acm.hdu.edu.cn/showproblem.php?pid=2062

题意：求n个数集合的第m个子序列，按字典序排序，也就是说1 2 < 1 2 3 < 1 3。

代码：

# include <stdio.h>
# include <string.h>


typedef long long ll ;
ll n, m, dp[25] = {0, 1} ;
int visited[25] ;
int flag ;


void init()
{
    int i ;
    for (i = 2 ; i <= 20 ; i++)
        dp[i] = 1 + dp[i-1]* (i-1) ;
}


int find(int idx)
{
    int i, cnt = 0 ;
    for (i = 1 ; ; i++)
    {
        if (visited[i] == 0)
            cnt++ ;
        if (cnt == idx){
            visited[i] = 1 ;
            return i ;
        }
    }
    return -1 ;
}


void output (ll n, ll m)
{
    ll idx = (m-1)/dp[n] + 1 ;
    if (flag == 0) flag = 1 ;
    else printf (" ") ;
    printf ("%d", find(idx)) ;
    if (n == 1 || m%dp[n] == 1) return ;
    output(n-1, (m-1)%dp[n]) ;
}


int main ()
{
    init () ;
    while (~scanf ("%I64d%I64d", &n, &m))
    {
        flag = 0 ;
        memset(visited, 0, sizeof(visited)) ;
        output(n,m) ;
        printf ("\n") ;
    }
    return 0 ;
}