Sorting It All Out - poj 1094 (拓扑排序)
Time Limit: 1000MS | Memory Limit: 10000K | |
Total Submissions: 29855 | Accepted: 10341 |
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.
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.
1 #include <iostream> 2 using namespace std; 3 int map[27][27]; 4 int point_num,edge_num; 5 int degree[27]; 6 char order[27]; 7 int top_sort(){ 8 int flag=1; 9 int p=-1; 10 for(int j=0;j<27;j++){ 11 degree[j]=0; 12 order[j]='\0'; 13 } 14 for(int i=0;i<point_num;i++){ 15 for(int j=0;j<point_num;j++){ 16 if(map[i][j])degree[j]++; 17 } 18 } 19 20 for(int i=0;i<point_num;i++){ 21 p=-1; 22 for(int j=0;j<point_num;j++){ 23 if(degree[j]==0){ 24 if(p==-1) p=j; 25 else flag=0; 26 } 27 } 28 if(p==-1) return 0; 29 degree[p]=-1; 30 order[i]=p+'A'; 31 for(int j=0;j<point_num;j++) 32 { 33 if(map[p][j]) degree[j]--; 34 } 35 } 36 if(flag) return 1; 37 else return 2; 38 } 39 int main() { 40 cin>>point_num>>edge_num; 41 while(point_num&&edge_num){ 42 int flag=0; 43 for(int i=0;i<27;i++){ 44 for(int j=0;j<27;j++){ 45 map[i][j]=0; 46 } 47 } 48 for(int i=0;i<edge_num;i++){ 49 char a,b,c; 50 cin>>a>>b>>c; 51 if(flag) continue; 52 map[a-'A'][c-'A']=1; 53 int result=top_sort(); 54 if(result==0){ 55 cout<<"Inconsistency found after "<<i+1<<" relations.\n"; 56 flag=1; 57 } 58 else if(result==1) 59 { 60 cout<<"Sorted sequence determined after "<<i+1<<" relations: "<<order<<".\n"; 61 flag=1; 62 } 63 } 64 if(!flag) cout<<"Sorted sequence cannot be determined.\n"; 65 cin>>point_num>>edge_num; 66 } 67 return 0; 68 }