[POJ](1094)Sorting It All Out ---拓扑排序(图)
Sorting It All Out
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 |
解题新知:(*@ο@*) 哇~这道题看了好长时间,理解题意是关键,还要注意题意情况的优先级关系。/(ㄒoㄒ)/~~不说了,还是看前辈们的思路和做法吧。自己也是稍微理解,稍微改了改前辈的代码。
参考:http://www.cnblogs.com/pushing-my-way/archive/2012/08/23/2652033.html
AC代码:
#include<iostream> #include<cstring> #include<cstdio> #include<algorithm> #include<queue> using namespace std; int mmap[30][30]; int indegree[30]; //int copyindegree[30]; int llist[30]; int n,m; int topoSort() { queue<int>q; int copyindegree[30]; for(int i=0;i<n;i++) { copyindegree[i]=indegree[i]; if(!indegree[i]) q.push(i); } int flag=0; int num=0; int k=-1; while(!q.empty()) { if(q.size()>1) flag=1; k=q.front(); q.pop(); llist[num++]=k; for(int i=0;i<n;i++) { if(mmap[k][i]==1) { copyindegree[i]--; if(copyindegree[i]==0) q.push(i); } } } if(num!=n) return 1; else if(flag) return 2; return 0; } int main() { while(cin>>n>>m && n && m) { int determined=0;//唯一升序序列确定 int inconsistency=0;//矛盾 char s[5]; int u,v; int res; memset(mmap,0,sizeof(mmap)); memset(indegree,0,sizeof(indegree)); memset(llist,0,sizeof(llist)); for(int i=1;i<=m;i++) { cin>>s; u=s[0]-'A'; v=s[2]-'A'; if(!determined && !inconsistency) { if(mmap[v][u]==1) { inconsistency=1; printf("Inconsistency found after %d relations.\n",i); continue;//??? } if(mmap[u][v]==0) { mmap[u][v]=1; indegree[v]++; } res=topoSort(); if(res==0) { printf("Sorted sequence determined after %d relations: ",i); for(int j=0;j<n;j++) printf("%c",llist[j]+'A'); printf(".\n"); determined=1; } else if(res==1) { printf("Inconsistency found after %d relations.\n",i); inconsistency=1; } } } if(!determined && !inconsistency) { printf("Sorted sequence cannot be determined.\n"); } } return 0; }