No.3 - POJ1094 拓扑排序

拓扑排序：

// ShellDawn
// POJ1094
// No.3

#include<algorithm>
#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#define MM(x) memset(x,0,sizeof(x));
using namespace std;

#define maxn 30
int n,m;
int E[maxn][maxn];
int V[maxn];
int v[maxn];
queue<int> ans;

int solve(){
    memcpy(v,V,sizeof(V));
    while(!ans.empty()) ans.pop();
    int cnt = 0;
    bool flag = true;
    int s = n;
    queue<int> q;
    while(s>0){
        //printf("<%d>\n",s);
        //for(int i=0;i<n;i++) printf("%d%s",v[i],i==n-1?"\n":" ");
        cnt = 0;
        for(int i=0;i<n;i++){
            if(v[i] == 0){
                s--;
                ans.push(i);
                q.push(i);
                v[i] = -1;
                cnt++;
            }
        }
        if(cnt == 0){
            return -1; // 环
        }
        if(cnt > 1){
            flag = false;  // 不确定
        }
        while(!q.empty()){
            int loc = q.front();
            q.pop();
            for(int i=0;i<n;i++){
                if(E[loc][i] == 1){
                    v[i] -- ;
                }
            }
        }
    }
    if(flag) return 1; // 有序
    return 0; // 不确定
}

int main(){
    while(scanf("%d%d",&n,&m)&&n!=0){
        MM(E);
        MM(V);
        bool flag = false;
        for(int i=0;i<m;i++){
            string s;
            cin>>s;
            if(flag) continue;
            int a = s[0] - 'A';
            int b = s[2] - 'A';
            if(E[a][b] == 0){
                E[a][b] = 1;
                V[b]++;
            }
            int S = solve();
            if(S == 1){ // 有序
                flag = true;
                printf("Sorted sequence determined after %d relations: ",i+1);
                while(!ans.empty()){
                    printf("%c",ans.front()+'A');
                    ans.pop();
                }
                puts(".");
                continue;
            }
            if(S == -1){ // 环
                flag = true;
                printf("Inconsistency found after %d relations.\n",i+1);
                continue;
            }
        }
        if(!flag){
            puts("Sorted sequence cannot be determined.");
        }
    }
    return 0;
}