POJ1094 Sorting It All Out

有向图找环

#include<cstdio>
#include<cstring>
int map[27][27],indegree[27],q[27];
int TopoSort(int n){
    int t=0,temp[27],p,m,flag=1;  //flag=1:有序 flag=-1:不确定
    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++,p=j;//查找入度为零的顶点个数
        if(m==0)return 0; //有环
        if(m>1) flag=-1;  //无序
        q[++t]=p,temp[p]=-1;//入度为零的点入队
        for(int j=1;j<=n;j++)if(map[p][j]==1)temp[j]--;
    }
    return flag;
}
int main(){
    int n,m,sign,x,y;
    for(char s[5];scanf("%d%d",&n,&m)!=EOF;){
        if(n==0&&m==0)break;
        memset(map,0,sizeof(map)),sign=0;
        memset(indegree,0,sizeof(indegree));
        for(int i=1;i<=m;i++){
            scanf("%s",s);
            if(sign)continue;
            x=s[0]-'A'+1,y=s[2]-'A'+1;
            map[x][y]=1,indegree[y]++;
            int f=TopoSort(n);
            if(f==0)sign=1,printf("Inconsistency found after %d relations.
",i);
            if(f==1){
                sign=1,printf("Sorted sequence determined after %d relations: ",i);
                for(int j=1;j<=n;j++)printf("%c",q[j]+'A'-1);
                puts(".");
            }
        }
        if(!sign)puts("Sorted sequence cannot be determined.");
    }
    return 0;
}

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 30;
int n, m, d[N][N], e[N][N];
 
int floyd() {
    memcpy(e, d, sizeof(e));
    for (int k = 0; k < n; k++)
        for (int i = 0; i < n; i++)
            for (int j = 0; j < n; j++) {
                e[i][j] |= e[i][k] & e[k][j];
                if (e[i][j] == e[j][i] && e[i][j] && i != j) return -1;
            }
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            if (e[i][j] == e[j][i] && !e[i][j] && i != j) return 0;
    return 1;
}
 
void Sorting_It_All_Out() {
    memset(d, 0, sizeof(d));
    bool flag = 1;
    for (int i = 1; i <= m; i++) {
        char s[6];
        scanf("%s", s);
        d[s[0]-'A'][s[2]-'A'] = 1;
        if (flag) {
            int now = floyd();
            if (now == -1) {
                printf("Inconsistency found after %d relations.
", i);
                flag = 0;
            } else if (now == 1) {
                printf("Sorted sequence determined after %d relations: ", i);
                pair<int, char> ans[N];
                for (int j = 0; j < n; j++) {
                    ans[j].first = 0;
                    ans[j].second = 'A' + j;
                }
                for (int j = 0; j < n; j++)
                    for (int k = 0; k < n; k++)
                        if (e[j][k]) ++ans[j].first;
                sort(ans, ans + n);
                for (int j = n - 1; j >= 0; j--) printf("%c", ans[j].second);
                puts(".");
                flag = 0;
            }
        }
    }
    if (flag) puts("Sorted sequence cannot be determined.");
}
 
int main() {
    while (cin >> n >> m && n) Sorting_It_All_Out();
    return 0;
}