2013
12-09

# Lotto

In a Lotto I have ever played, one has to select 6 numbers from the set {1,2,…,49}. A popular strategy to play Lotto – although it doesn’t increase your chance of winning – is to select a subset S containing k (k>6) of these 49 numbers, and then play several games with choosing numbers only from S. For example, for k=8 and S = {1,2,3,5,8,13,21,34} there are 28 possible games: [1,2,3,5,8,13], [1,2,3,5,8,21], [1,2,3,5,8,34], [1,2,3,5,13,21], … [3,5,8,13,21,34].

Your job is to write a program that reads in the number k and the set S and then prints all possible games choosing numbers only from S.

The input file will contain one or more test cases. Each test case consists of one line containing several integers separated from each other by spaces. The first integer on the line will be the number k (6 < k < 13). Then k integers, specifying the set S, will follow in ascending order. Input will be terminated by a value of zero (0) for k.

For each test case, print all possible games, each game on one line. The numbers of each game have to be sorted in ascending order and separated from each other by exactly one space. The games themselves have to be sorted lexicographically, that means sorted by the lowest number first, then by the second lowest and so on, as demonstrated in the sample output below. The test cases have to be separated from each other by exactly one blank line. Do not put a blank line after the last test case.

7 1 2 3 4 5 6 7
8 1 2 3 5 8 13 21 34
0

1 2 3 4 5 6
1 2 3 4 5 7
1 2 3 4 6 7
1 2 3 5 6 7
1 2 4 5 6 7
1 3 4 5 6 7
2 3 4 5 6 7

1 2 3 5 8 13
1 2 3 5 8 21
1 2 3 5 8 34
1 2 3 5 13 21
1 2 3 5 13 34
1 2 3 5 21 34
1 2 3 8 13 21
1 2 3 8 13 34
1 2 3 8 21 34
1 2 3 13 21 34
1 2 5 8 13 21
1 2 5 8 13 34
1 2 5 8 21 34
1 2 5 13 21 34
1 2 8 13 21 34
1 3 5 8 13 21
1 3 5 8 13 34
1 3 5 8 21 34
1 3 5 13 21 34
1 3 8 13 21 34
1 5 8 13 21 34
2 3 5 8 13 21
2 3 5 8 13 34
2 3 5 8 21 34
2 3 5 13 21 34
2 3 8 13 21 34
2 5 8 13 21 34
3 5 8 13 21 34

mark：直接dfs就好了。

# include <stdio.h>

int k ;
int num[20] ;
int ans[6] ;

void dfs(int idx, int n)
{
int i ;
if (n == 6)
{
for(i = 0 ; i < n ; i++)
if (i == 0) printf("%d",ans[i]) ;
else printf (" %d", ans[i]) ;
printf ("\n") ;
return ;
}
for (i = idx ; i < k + n - 5; i++)
{
ans[n] = num[i] ;
dfs(i+1,n+1) ;
}
}

int main ()
{
int i ;
int flag = 0 ;
while (~scanf ("%d", &k),k)
{
for(i=0;i<k;i++) scanf("%d", &num[i]) ;
if (flag == 0) flag = 1;
else printf ("\n") ;
dfs (0,0) ;
}
return 0 ;
}

1. 换句话说，A[k/2-1]不可能大于两数组合并之后的第k小值，所以我们可以将其抛弃。
应该是，不可能小于合并后的第K小值吧