Sorting It All Out
Time Limit: 1000MS Memory Limit: 10000K
Total Submissions: 37417 Accepted: 13220
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.
Source
East Central North America 2001
最失败的题之一,调了太久,很难受。
topo()的返回值写成bool,查良久,无果。。
本质就是拓扑排序,把字母当成节点,建图,不过加入了几个特殊的条件,有环或者无法完全排序都是特殊情况,要特殊判断,但是判断完了剩下的数据仍然得输入。
然后输出的部分,句号什么的,很难受。写的时候也是很混乱..
可能今天心情不好…
//Stay foolish,stay hungry,stay young,stay simple
#include<iostream>
#include<queue>
#include<cstdio>
#include<cstring>
using namespace std;
const int MAXN=20000;
int n,m;
struct Edge{
int next,to;
}e[MAXN];
int ecnt,head[MAXN],ind[MAXN];
inline void add(int x,int y){
e[++ecnt].next = head[x];
e[ecnt].to = y;
head[x] = ecnt;
}
int tmp[MAXN];
int ans[MAXN],anscnt;
int topo(){
anscnt=0;
memcpy(tmp,ind,sizeof(ind));
int ret=1;
for(int i=1;i<=n;i++){
int cnt=0,pos;
for(int j=1;j<=n;j++)
if(tmp[j]==0) cnt++,pos=j;
if(cnt==0) return 0;//circle
if(cnt>1) ret=-1;//unsure
tmp[pos]=-1;//
ans[++anscnt]=pos;
for(int j=head[pos];j;j=e[j].next){
int v=e[j].to;
tmp[v]--;
}
}
return ret;
}
void slove(){
bool succ=0;
for(int i=1;i<=m;i++){
char s[5];
cin>>s;
if(succ) continue;
int x=s[0]-'A'+1;
int y=s[2]-'A'+1;
add(x,y);
ind[y]++;
int res=topo();
if(res==0){
printf("Inconsistency found after %d relations.
",i);
succ=1;
}
if(res==1){
printf("Sorted sequence determined after %d relations: ",i);
for(int j=1;j<=anscnt;j++) cout<<char(ans[j]+'A'-1);
printf(".
");
succ=1;//
}
}
if(!succ) printf("Sorted sequence cannot be determined.
");
}
int main(){
// freopen("test.txt","r",stdin);
while(cin>>n>>m&&n){
ecnt=0,anscnt=0;
memset(head,0,sizeof(head));
memset(ind,0,sizeof(ind));
slove();
}
return 0;
}