delete pics to save space

7.1094.cpp

@@ -0,0 +1,54 @@
+#include<cstdio>
+#include<cstring>
+#include<algorithm>
+#include<queue>
+#include<cassert>
+using namespace std;
+const int maxn=30;
+int n,m,d[maxn][maxn],in[maxn];
+char s[maxn][4];
+int solve(int m)
+{
+	memset(d,0,sizeof(d));
+	for(int i=1;i<=m;i++) d[s[i][0]-'A'+1][s[i][2]-'A'+1]=1;
+	for(int k=1;k<=n;k++)
+		for(int i=1;i<=n;i++)
+			for(int j=1;j<=n;j++)
+				d[i][j]|=d[i][k]&d[k][j];
+	for(int i=1;i<=n;i++)	
+		for(int j=1;j<=n;j++)
+			if(d[i][j]&&d[j][i]) { printf("Inconsistency found after %d relations.\n",m); return 1; }
+	for(int i=1;i<=n;i++) for(int j=1;j<=n;j++) if(i!=j&&d[i][j]+d[j][i]==0) return 0;
+	printf("Sorted sequence determined after %d relations: ",m);
+	for(int i=1;i<=n;i++) for(int j=1;j<=n;j++) if(d[i][j]) in[j]++;
+	queue<int> Q;
+	for(int i=1;i<=n;i++) if(in[i]==0) Q.push(i);
+	assert(Q.size()==1);
+	while(Q.size())
+	{
+		int u=Q.front(); Q.pop();
+		printf("%c",char(u-1+'A'));
+		for(int i=1;i<=n;i++) if(d[u][i])
+		{
+			d[u][i]=0;
+			in[i]--;
+			if(in[i]==0) Q.push(i);
+		}
+	}
+	puts(".");
+	return 1;
+}
+int main()
+{
+	#ifdef local
+	freopen("pro.in","r",stdin);
+	#endif
+	while(scanf("%d%d",&n,&m)==2&&n+m)
+	{
+		for(int i=1;i<=m;i++) scanf("%s",s[i]);
+		for(int i=1;i<=m;i++) if(solve(i)) goto nxt;
+		puts("Sorted sequence cannot be determined.");
+		nxt:continue;
+	}
+	return 0;
+}