POJ1094 Sorting It All Out

Posted 2021-02-06 lzxzy-blog

 

 

　　　　　　　　　　　　　　Sorting It All Out

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 40012		Accepted: 14072

Description

An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from smallest to largest. For example, the sorted sequence A, B, C, D implies that A < B, B < C and C < D. in this problem, we will give you a set of relations of the form A < B and ask you to determine whether a sorted order has been specified or not.

Input

Input consists of multiple problem instances. Each instance starts with a line containing two positive integers n and m. the first value indicated the number of objects to sort, where 2 <= n <= 26. The objects to be sorted will be the first n characters of the uppercase alphabet. The second value m indicates the number of relations of the form A < B which will be given in this problem instance. Next will be m lines, each containing one such relation consisting of three characters: an uppercase letter, the character "<" and a second uppercase letter. No letter will be outside the range of the first n letters of the alphabet. Values of n = m = 0 indicate end of input.

Output

For each problem instance, output consists of one line. This line should be one of the following three: 

Sorted sequence determined after xxx relations: yyy...y. 
Sorted sequence cannot be determined. 
Inconsistency found after xxx relations. 

where xxx is the number of relations processed at the time either a sorted sequence is determined or an inconsistency is found, whichever comes first, and yyy...y is the sorted, ascending sequence. 

Sample Input

4 6
A<B
A<C
B<C
C<D
B<D
A<B
3 2
A<B
B<A
26 1
A<Z
0 0

Sample Output

 

Sorted sequence determined after 4 relations: ABCD.
Inconsistency found after 2 relations.
Sorted sequence cannot be determined.

---------------------------------------------------------分界线------------------------------------------------------------------------

由题目描述可知：

　　该题 典型的拓扑排序。

　　1、在 拓扑排序时，当出现同时可访问两个节点或多个节点时，则信息不完全。

　　2、当出现有环时，则有冲突，判断是否有环可以在拓扑排序完时判断是否有点未访问。因为若无环，每个点都可以访问。

 

不多说了，附上我的AC代码：

 1 #include <queue>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <iostream>
 5 using namespace std;
 6 const int MAXN=2500;
 7 int n,m,cas,id;
 8 
 9 struct edge
10 {
11     int v,nx;
12 }set[MAXN];
13 int head[30],d[30],ok[30],write[30];
14 queue<int> Q;
15 
16 void Addedge(int u,int v)
17 {
18     id++;set[id].v=v;set[id].nx=head[u];
19     head[u]=id;
20 }
21 
22 int bfs()
23 {
24     cas=0;
25     while(!Q.empty())Q.pop();
26     int out=1,t,u;t=0;
27     for(int i=1;i<=n;i++)
28         if(!ok[i])
29         {
30             t++;Q.push(i);
31         }
32     if(t>1)out=0;
33     while(!Q.empty())
34     {
35         u=Q.front();Q.pop();t=0;write[++cas]=u;
36         for(int k=head[u];k>0;k=set[k].nx)
37         {
38             ok[set[k].v]--;
39             if(!ok[set[k].v])
40             {
41                 t++;Q.push(set[k].v);
42             }
43         }
44         if(t>1)out=0;
45     }
46     for(int i=1;i<=n;i++)if(ok[i]>0){out=-1;break;}
47     return out;
48 }
49 
50 char print()
51 {
52     for(int i=1;i<=cas;i++)printf("%c",(char)(write[i]+64));
53     return ‘.‘;    
54 }
55 
56 int main()
57 {
58     while(~scanf("%d%d",&n,&m))
59     {
60         memset(write,0,sizeof(write));    
61         memset(d,0,sizeof(d));    
62         memset(head,-1,sizeof(head));
63         id=0;
64         int now=0,loca;
65         char a,b,c;
66         if(n==0 && m==0)break;
67         for(int i=1;i<=m;i++)
68         {
69             cin>>a>>b>>c;
70             if(b==‘<‘)
71             {
72                 Addedge(a-64,c-64);d[c-64]++;
73             }
74             else 
75             {
76                 Addedge(c-64,a-64);d[a-64]++;
77             }
78             if(now==0)
79             {
80                 for(int j=1;j<=n;j++)ok[j]=d[j];
81                 now=bfs();loca=i;
82             }
83         }
84         if(now==0)puts("Sorted sequence cannot be determined.");
85         else if(now==1)printf("Sorted sequence determined after %d relations: ",loca),printf("%c
",print());
86         else printf("Inconsistency found after %d relations.
",loca);
87     }
88     return 0;
89 }

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