hdu 2611 Sequence two(深搜)

Sequence two

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 98 Accepted Submission(s): 46

Problem Description

Search is important in the acm algorithm. When you want to solve a problem by using the search method, try to cut is very important.
Now give you a number sequence, include n (<=100) integers, each integer not bigger than 2^31, you want to find the first P subsequences that is not decrease (if total subsequence W is smaller than P, than just give the first W subsequences). The order of subsequences is that: first order the length of the subsequence. Second order the subsequence by lexicographical. For example initial sequence 1 3 2 the total legal subsequences is 5. According to order is {1}; {2}; {3}; {1,2}; {1,3}. If you also can not understand , please see the sample carefully.

 

Input

The input contains multiple test cases.
Each test case include, first two integers n, P. (1<n<=100, 1<p<=100000).

 

Output

For each test case output the sequences according to the problem description. And at the end of each case follow a empty line.

 

Sample Input

3 5
1 3 2
3 6
1 3 2
4 100
1 2 3 2

 

Sample Output

1
2
3
1 2
1 3

1
2
3
1 2
1 3

1
2
3
1 2
1 3
2 2
2 3
1 2 2
1 2 3

Hint

Hint : You must make sure each subsequence in the subsequences is unique

分析:

（1）这道题和前一题sequence one 属于一类题，都是dfs,这里主要是首先排一次顺序，然后再检查时注意输入时的下标，生成的子串不能够出现下表非递增的，也就是首先子串时递增的，其次下标也是递增的，然后不能有重复的子串出现。

（2）这是我的代码，和前一题的代码有稍微的改动，无奈一直wrong。。。。。。。。。。。。哪位研究这一题的看到了，帮忙找找错。。。。。。。。。

 

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
using namespace std;

//len:搜索的长度,count:记录有多少个串了
int n,p,len,count_num,pre;

//做一个标记，如果一个短的串都不能够找到，
//那么就长的串就更不可能找到了，这里的一个巧妙地剪枝如果没用就会超时
bool flag;

typedef struct
{
    int n,pos;
    int ind;
}Tem;

Tem tem[1001];
Tem num[1001];

bool cmp(Tem a,Tem b)
{
    if(a.n==b.n)
    return a.pos<b.pos;
    return a.n<b.n;
}
//若在产生序列的前一个数字到当前这个数字中，
//出现等于num[e]的，那么说明之前已经有序列选择了num[e]，
bool check(int s,int e)
{
    for(int i = e-1; i > s; i--)
    if(num[i].n==num[e].n)return false;
    return true;
}


void print_sequence(int length)
{
    for(int i = 0; i < length-1;i++)
    printf("%d ",tem[i].n);
    printf("%d\n",tem[length-1].n);
}

//dep：搜索的深度，也就是目前搜索到子串的长度
//pos: 当前搜索的位置
void dfs(int dep,int pos)
{
    if(count_num >= p)return;
    //搜索到了
    if(dep==len)
    {
        count_num++;
        flag = true;
        print_sequence(len);
        //已经搜索到符合的字串了
        return;
    }
    for(int i=pos;i<n;i++)
    {
        if((dep!=0&&num[i].pos>tem[dep-1].pos)||dep==0)
        {
            if(dep==0&&!check(-1,i))
            continue;
            if(dep!=0&&!check(tem[dep-1].ind,i))
            continue;
            tem[dep].n = num[i].n;
            tem[dep].pos = num[i].pos;
            tem[dep].ind = i;
            dfs(dep+1,i+1);
        }
    }
    return;
}

int main()
{
    while(scanf("%d%d",&n,&p)!=EOF)
    {
        for(int i=0;i<n;i++)
        {
            scanf("%d",&num[i].n);
            num[i].pos = i;
        }

        sort(num,num+n,cmp);
        count_num = 0;
        for(int i = 1;i < n;i++)
        {
            flag=false;
            pre = 0;
            len = i;
            dfs(0,0);
            if(count_num>=p||!flag)break;
        }
        printf("\n");
    }
    return 0;
}

这是我从网上找到达一个可以通过的代码。。。。。。

思路一样。。。。。。。求解释。。。。。。。

#include <cstdio>
#include <queue>
#include <cstring>
#include <algorithm>

using namespace std;

int n,p;

struct Node
{
        int pos;
        int v;
};

int cont;
Node a[110];
int res[10001];
int deep;

bool mcmp(const Node& x,const Node& y)
{
        if(x.v != y.v)
                return x.v < y.v;
        else
                return x.pos < y.pos;
};

void init()
{
        int i;
        int tv;
        cont = 0;
        Node tnode;
        for(i = 1;i <= n;i ++)
        {
                scanf("%d",&tv);
                a[i].pos = i;// 把位置作为结构题的一项
                a[i].v = tv;
        }
        sort(a+1,a+1+n,mcmp);//按照值的大小重排序
}

bool dfs(int dep,int sp,int pp)//deepth ,search position , previous position
{
        int i;
        int prev;
        bool f = false;
        if(dep == deep+1)
        {
                cont ++;
                for(i = 1;i < dep;i ++)
                        printf(i == deep ? "%d\n" : "%d ",res[i]);
                if(cont == p) return true;
                return false;
        }

        if(sp > n ) return false;

        for(i = sp;i <= n;i ++)
        {
                if(a[i].pos > pp)
                {
                        if(!f) { f = true; prev = a[i].v;} // 判重
                        else        if(prev == a[i].v) continue;//判重
                        prev = a[i].v;
                        res[dep] = a[i].v;
                        if(dfs(dep+1,i+1,a[i].pos) ) return true;

                }
        }
        return false;
}

void work()
{
        int i,j;
        for(i = 1;i <= n;i ++)
        {
                deep = i;
                if(dfs(1,1,0)) return ;
        }
}

int main()
{
        while(scanf("%d%d",&n,&p) != EOF)
        {
                init();
                work();
                printf("\n");
        }

        return 0;
}