题目大意:将字母按照所给的序列从小到大输出。
算法思路:首先判断该图是否存在环,如果不存在,看能否进行有序输出,如果有序则后面的处理步骤都可以跳过,否则输出题目所给的话。
#include<iostream> #include<string> using namespace std; int n,m,indegree[30],map[30][30]; char ans[30]; int topusort() { int temp[30],sym=0,i,j,m,flag,res=1; for(i=0;i<n;i++) { temp[i]=indegree[i]; } for(i=0;i<n;i++) { m=0; for(j=0;j<n;j++) { if(temp[j]==0) { m++; flag=j; } } if(m==0)//说明有环 return 0; if(m>1) res=-1; ans[sym++]=flag+'A'; temp[flag]=-1; for(j=0;j<n;j++) { if(map[flag][j]>0) temp[j]--; } } return res; } int main() { int i,j,sign; string s; while(scanf("%d%d",&n,&m)&&(n!=0||m!=0)) { sign=0; memset(ans,0,sizeof(ans)); memset(map,0,sizeof(map)); memset(indegree,0,sizeof(indegree)); for(i=1;i<=m;i++) { cin>>s; if(sign) continue; int x=s[0]-'A'; int y=s[2]-'A'; map[x][y]=1; indegree[y]++; int ss=topusort(); if(ss==0)//有环 { cout<<"Inconsistency found after "<<i<<" relations."<<endl; sign=1; } if(ss==1)//有序 { cout<<"Sorted sequence determined after "<<i<<" relations: "; for(j=0;j<n;j++) { cout<<ans[j]; } cout<<"."<<endl; sign=1; } } if(!sign) cout<<"Sorted sequence cannot be determined."<<endl; } }