Sorting It All Out(拓撲排序)
阿新 • • 發佈:2017-12-02
stream ecif nco define 根據 判斷 values ges cond
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.
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.
題目:
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
Output
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.
題意:輸入n,m,n和m為0的時候輸入結束,n代表n個字母,接下來輸入m組數據,然後讓你根據這m組數據判斷是否能將這m個字母排序好,要註意在第i組數據能排序好的時候就輸出結果,接下來的數據值輸入,不進行判斷;
分析:這是我第一次做有於拓撲排序有關的題目,根據題意我們需要分為三步:①判斷是否形成循環 ②判斷是否有序 ③無法判斷(題目輸入的數據不足以判斷)
AC代碼:
#include<iostream> #include<cstdio> #include<string> #include<cstring> #include<cmath> #include<algorithm> using namespace std; #define N 30 char Map[N][N]; int indegree[N],p[N]; int c; int toposort(int n) { c=0; int sign=1; int temp[N],m,now; for (int i=1;i<=n;i++) temp[i]=indegree[i]; for (int i=1;i<=n;i++) { m=0; for (int j=1;j<=n;j++) if (temp[j]==0) m++,now=j; if (m==0) return 0; //成環 if (m>1) sign=-1; //無法判斷 p[c++]=now; temp[now]=-1; for (int j=1;j<=n;j++) if (Map[now][j]==1) temp[j]--; } return sign; //有序 } int main() { int n,m; char w[5]; int x,y; while (scanf("%d%d",&n,&m)&&(n!=0||m!=0)) { int flag=0; memset(Map,0,sizeof(Map)); memset(indegree,0,sizeof(indegree)); for (int i=1;i<=m;i++) { scanf("%s",w); if (flag) continue; x=w[0]-‘A‘+1; y=w[2]-‘A‘+1; Map[x][y]=1; //x->y indegree[y]++; //後者入度+1 int t=toposort(n); if (t==0) printf("Inconsistency found after %d relations.\n",i),flag=1; else if (t==1) { printf("Sorted sequence determined after %d relations: ",i); for(int j=0;j<c;j++) printf("%c",p[j]+‘A‘-1); printf(".\n"); flag=1; } } if (!flag) printf("Sorted sequence cannot be determined.\n"); } return 0; }
Sorting It All Out(拓撲排序)