poj2245Lotto(最基础的dfs)

题目链接：

啊哈哈，点我点我

思路：最開始画好搜索状态，然后找好结束条件，最好预推断当前找到的个数和能够找到的是否大于6就可以。。

题目：

Lotto

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 6291		Accepted: 3995

Description

In the German Lotto you have 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. 

Input

The input 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.

Output

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.

Sample Input

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

Sample Output

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

Source

Ulm Local 1996

代码为：

#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
const int maxn=50+10;
int a[maxn],n,ans[maxn];

void dfs(int ith,int num)
{
    if(num==6)
    {
        for(int i=1;i<=5;i++)
              printf("%d ",ans[i]);
        printf("%d\n",ans[6]);
        return;
    }
    //if(num+n-ith<6)  return;
    for(int ai=ith+1;i<=n;i++)
    {
        ans[num+1]=a[i];
        dfs(i,num+1);
    }
}

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