POJ 1094 Sorting It All Out 拓扑排序 难度:0
http://poj.org/problem?id=1094
#include <cstdio> #include <cstring> #include <vector> using namespace std; int in[27],out[27]; char index[27]; bool vis[27]; int mem[27][27]; int n,m; int tlen; bool floyd(){ for(int i=0;i<n;i++){ for(int j=0;j<n;j++){ for(int k=0;k<n;k++){ if(mem[i][k]&&mem[k][j])mem[i][j]=1; } } } for(int i=1;i<n;i++){ if(mem[i][i])return false; } return true; } bool calc(){ memset(in,0,sizeof(in)); memset(out,0,sizeof(out)); for(int i=0;i<n;i++){ for(int j=0;j<n;j++){ if(mem[i][j]==1){ out[i]++; in[j]++; }} } for(int i=0;i<n;i++){ if(in[i]+out[i]!=n-1)return false; } return true; } bool topologicalsort(){ memset(vis,0,sizeof(vis)); int len=0; bool fl=false; while(len<n){ fl=false; for(int i=0;i<n;i++){ if(in[i]==0&&!vis[i]){ fl=true; vis[i]=true; index[len]=i+'A'; len++; for(int j=0;j<n;j++){ if(mem[i][j])in[j]--; } break; } } if(!fl)return false; } return true; } int main(){ char ch,ch2; while (scanf("%d %d",&n,&m)==2&&n){ bool fl=false; getchar(); memset(mem,0,sizeof(mem)); memset(index,0,sizeof(index)); for(int i=1;i<=m;i++){ scanf(" %c< %c",&ch,&ch2); in[ch2-'A']++; out[ch-'A']++; mem[ch-'A'][ch2-'A']=1; getchar(); if(fl)continue; if(floyd()){ if(calc()){ if(topologicalsort()){ fl=true; index[n]=0; printf("Sorted sequence determined after %d relations: %s.\n",i,index); continue; } } } else { printf("Inconsistency found after %d relations.\n",i); fl=true; continue; } } if(!fl)printf("Sorted sequence cannot be determined.\n"); } return 0; }