hdu 2160 Sequence one（DFS）

#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <memory.h>
using namespace std;
#define MAXN 20002


//适用于正整数
template <class T>
inline void scan_d(T &ret) {
    char c; ret=0;
    while((c=getchar())<'0'||c>'9');
    while(c>='0'&&c<='9') ret=ret*10+(c-'0'),c=getchar();
}

int a[1010];
int cnt;
int ans[1010];
int tot;
int n, k;
int flag;

int check(int i,int j)           //检查是否有出现过的数字
{
    while (i < j)
        if (a[i++] == a[j])
        return 0;
    return 1;
}

void dfs(int now, int num)
{
    int i;
    if (num == tot) {
        ++cnt;
        for (i = 0;i < tot-1; ++ i)
            printf("%d ",ans[i]);
        printf("%d
",ans[tot-1]);
        if (cnt == k) flag = 1;
        return;
    }
    if (num == 0) {                              //第一次不存在前一个数，特殊处理
        for (i = 0;i < n; ++ i) {
            if (check(0,i)) {
                ans[num] = a[i];
                dfs(i,1);
                if (flag) return;
            }
        }
    } else {
        for (i = now + 1;i < n; ++ i) {
            if (a[i] >= a[now] && check(now+1,i)) {
                ans[num] = a[i];
                dfs(i,num + 1);
                if (flag) return;
            }
        }
    }
}

int main()
{
    int i, t;
    while (~scanf("%d%d",&n,&k)) {
        for (i = 0;i < n; ++ i)
            scan_d(a[i]);
        cnt = 0;
        for (tot = 1;cnt < k; ++ tot) {
            flag = 0;
            t = cnt;
            dfs(0,0);
            if (t == cnt || flag) break;              //达到要求个数或者输出完所有可能情况结束
        }
        puts("");
    }
    return 0;
}