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test32.c
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test32.c
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#include <stdio.h>
#include <string.h>
#define MAX 100
int ans[MAX];
int v[MAX];
int G[MAX][MAX];
int t;
int n;
int dfs(int u)
{
v[u] = -1;
int i;
for(i = 0; i < n; i++)
{
if(G[u][i])
{
if (v[i] == -1) return 0;
else if(!v[i] && !dfs(i)) return 0;
}
}
v[u] = 1;
ans[--t] = u;
return 1;
}
int top_sort()
{
memset(v, 0, sizeof(v));
int i;
for(i = 0; i < n; i++)
{
if(!v[i] && !dfs(i)) return 0;
}
return 1;
}
int main(int argc, char** argv)
{
int m;
int i;
char s[4];
while(scanf("%d%d", &n, &m) == 2)
{
t = n;
memset(G, 0, sizeof(G));
for(i = 0; i < m; i++)
{
scanf("%s", s);
G[s[0]-'a'][s[2]-'a'] = 1;
}
if(top_sort())
{
for(i = 0; i < n; i++)
printf("%c ", 'a'+ans[i]);
printf("\n");
}
else printf("-1\n");
}
return 0;
}