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;
}